cmd/go: fix wording issue in comment

golang.org/cl/157097 modified this comment, but left a trailing comma.
While at it, make the sentence a bit clearer.

Change-Id: I376dda4fd18ddbcae4485dd660a79b9f66ad6da4
Reviewed-on: https://go-review.googlesource.com/c/158037Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/internal/modload/build.go

@@ -252,7 +252,7 @@ func findModule(target, path string) module.Version {
 func ModInfoProg(info string) []byte {
 	// Inject a variable with the debug information as runtime/debug.modinfo,
 	// but compile it in package main so that it is specific to the binary.
-	// No need to populate in an init func, it will still work with go:linkname,
+	// No need to populate it in an init func; it will still work with go:linkname.
 	return []byte(fmt.Sprintf(`package main
 import _ "unsafe"
 //go:linkname __debug_modinfo__ runtime/debug.modinfo