fix errors identified by staticcheck (#447)

internal/driver/commands.go

 		cmd := exec.Command("dot", "-T"+format)
 		cmd.Stdin, cmd.Stdout, cmd.Stderr = input, output, os.Stderr
 		if err := cmd.Run(); err != nil {
-			return fmt.Errorf("Failed to execute dot. Is Graphviz installed? Error: %v", err)
+			return fmt.Errorf("failed to execute dot. Is Graphviz installed? Error: %v", err)
 		}
 		return nil
 	}

internal/driver/driver_focus.go

 	}
 	v, err := strconv.ParseInt(ranges[0][1], 10, 64)
 	if err != nil {
-		panic(fmt.Errorf("Failed to parse int %s: %v", ranges[0][1], err))
+		panic(fmt.Errorf("failed to parse int %s: %v", ranges[0][1], err))
 	}
 	scaledValue, unit := measurement.Scale(v, ranges[0][2], ranges[0][2])
 	if len(ranges) == 1 {
 		return nil
 	}
 	if v, err = strconv.ParseInt(ranges[1][1], 10, 64); err != nil {
-		panic(fmt.Errorf("Failed to parse int %s: %v", ranges[1][1], err))
+		panic(fmt.Errorf("failed to parse int %s: %v", ranges[1][1], err))
 	}
 	scaledValue2, unit2 := measurement.Scale(v, ranges[1][2], unit)
 	if unit != unit2 {

internal/driver/interactive.go

 					}
 					continue
 				} else if okValues := groups[name]; okValues != nil {
-					o.UI.PrintErr(fmt.Errorf("Unrecognized value for %s: %q. Use one of %s", name, value, strings.Join(okValues, ", ")))
+					o.UI.PrintErr(fmt.Errorf("unrecognized value for %s: %q. Use one of %s", name, value, strings.Join(okValues, ", ")))
 					continue
 				}
 			}
 		}
 	}
 	if c == nil {
-		return nil, nil, fmt.Errorf("Unrecognized command: %q", name)
+		return nil, nil, fmt.Errorf("unrecognized command: %q", name)
 	}
 
 	if c.hasParam {
 			if outputFile == "" {
 				i++
 				if i >= len(args) {
-					return nil, nil, fmt.Errorf("Unexpected end of line after >")
+					return nil, nil, fmt.Errorf("unexpected end of line after >")
 				}
 				outputFile = args[i]
 			}

internal/driver/interactive_test.go

 	ui := &proftest.TestUI{
 		T:       t,
 		Input:   []string{"cumulative=this"},
-		AllowRx: `Unrecognized value for cumulative: "this". Use one of cum, flat`,
+		AllowRx: `unrecognized value for cumulative: "this". Use one of cum, flat`,
 	}
 	o.UI = ui
 	if err := interactive(p, o); err != nil {

internal/elfexec/elfexec.go

 			return start - *stextOffset, nil
 		}
 
-		return 0, fmt.Errorf("Don't know how to handle EXEC segment: %v start=0x%x limit=0x%x offset=0x%x", *loadSegment, start, limit, offset)
+		return 0, fmt.Errorf("don't know how to handle EXEC segment: %v start=0x%x limit=0x%x offset=0x%x", *loadSegment, start, limit, offset)
 	case elf.ET_REL:
 		if offset != 0 {
-			return 0, fmt.Errorf("Don't know how to handle mapping.Offset")
+			return 0, fmt.Errorf("don't know how to handle mapping.Offset")
 		}
 		return start, nil
 	case elf.ET_DYN:
 		// sx = x - start + offset - loadSegment.Off + loadSegment.Vaddr.
 		return start - offset + loadSegment.Off - loadSegment.Vaddr, nil
 	}
-	return 0, fmt.Errorf("Don't know how to handle FileHeader.Type %v", fh.Type)
+	return 0, fmt.Errorf("don't know how to handle FileHeader.Type %v", fh.Type)
 }
 
 // FindTextProgHeader finds the program segment header containing the .text

internal/measurement/measurement.go

 	case "year", "yr":
 		output, toUnit = dd/float64(365*24*time.Hour), "yrs"
 	default:
-		fallthrough
-	case "sec", "second", "s":
+		// "sec", "second", "s" handled by default case.
 		output, toUnit = dd/float64(time.Second), "s"
 	}
 	return output, toUnit, true

internal/proftest/proftest.go

 	input := ui.Input[ui.index]
 	ui.index++
 	if input == "**error**" {
-		return "", fmt.Errorf("Error: %s", input)
+		return "", fmt.Errorf("error: %s", input)
 	}
 	return input, nil
 }

internal/report/source.go

 	if sourcePath == "" {
 		wd, err := os.Getwd()
 		if err != nil {
-			return fmt.Errorf("Could not stat current dir: %v", err)
+			return fmt.Errorf("could not stat current dir: %v", err)
 		}
 		sourcePath = wd
 	}
 	if sourcePath == "" {
 		wd, err := os.Getwd()
 		if err != nil {
-			return fmt.Errorf("Could not stat current dir: %v", err)
+			return fmt.Errorf("could not stat current dir: %v", err)
 		}
 		sourcePath = wd
 	}
 	}
 
 	if len(fileNodes) == 0 {
-		return fmt.Errorf("No source information for %s", o.Symbol.String())
+		return fmt.Errorf("no source information for %s", o.Symbol.String())
 	}
 
 	sourceFiles := make(graph.Nodes, 0, len(fileNodes))
 		}
 	}
 
-	return nil, fmt.Errorf("Could not find file %s on path %s", path, searchPath)
+	return nil, fmt.Errorf("could not find file %s on path %s", path, searchPath)
 }
 
 // trimPath cleans up a path by removing prefixes that are commonly