fixed year unit conversion (#212)

* fixed year unit conversion

* added test for conversion to year

internal/measurement/measurement.go

 	case "week", "wk":
 		output, toUnit = dd/float64(7*24*time.Hour), "wks"
 	case "year", "yr":
-		output, toUnit = dd/float64(365*7*24*time.Hour), "yrs"
+		output, toUnit = dd/float64(365*24*time.Hour), "yrs"
 	default:
 		fallthrough
 	case "sec", "second", "s":

internal/measurement/measurement_test.go

 		{1024, "gb", "tb", 1, "TB"},
 		{1024, "tb", "pb", 1, "PB"},
 		{2048, "mb", "auto", 2, "GB"},
+		{3.1536e7, "s", "auto", 1, "yrs"},
 	} {
 		if gotValue, gotUnit := Scale(tc.value, tc.fromUnit, tc.toUnit); gotValue != tc.wantValue || gotUnit != tc.wantUnit {
 			t.Errorf("Scale(%d, %q, %q) = (%f, %q), want (%f, %q)",