internal: fix typos (#482)

internal/driver/webui.go

 		return nil, err
 	}
 
-	// Fix dot bug related to unquoted amperands.
+	// Fix dot bug related to unquoted ampersands.
 	svg := bytes.Replace(out.Bytes(), []byte("&;"), []byte("&;"), -1)
 
 	// Cleanup for embedding by dropping stuff before the <svg> start.

internal/graph/graph.go

 // works as a unique identifier; however, in a tree multiple nodes may share
 // identical NodeInfos. A *Node does uniquely identify a node so we can use that
 // instead. Though a *Node also uniquely identifies a node in a graph,
-// currently, during trimming, graphs are rebult from scratch using only the
+// currently, during trimming, graphs are rebuilt from scratch using only the
 // NodeSet, so there would not be the required context of the initial graph to
 // allow for the use of *Node.
 type NodePtrSet map[*Node]bool

internal/plugin/plugin.go

 	UI      UI
 
 	// HTTPServer is a function that should block serving http requests,
-	// including the handlers specfied in args.  If non-nil, pprof will
+	// including the handlers specified in args.  If non-nil, pprof will
 	// invoke this function if necessary to provide a web interface.
 	//
 	// If HTTPServer is nil, pprof will use its own internal HTTP server.