cmd/go/internal/vgo: fix comment of SrcMod

The local cache directory root from $GOPATH/src/v to $GOPATH/src/mod
in CL 119475.

Change-Id: I43a23eaf61df807bc8b98d8a251a0c6a39d18f29
Reviewed-on: https://go-review.googlesource.com/119496
Reviewed-by: Bryan C. Mills <bcmills@google.com>
diff --git a/vendor/cmd/go/internal/vgo/init.go b/vendor/cmd/go/internal/vgo/init.go
index ba8122f..f0ff6f7 100644
--- a/vendor/cmd/go/internal/vgo/init.go
+++ b/vendor/cmd/go/internal/vgo/init.go
@@ -40,7 +40,7 @@
 	Target   module.Version
 
 	gopath string
-	SrcMod string // GOPATH/src/v directory where versioned cache lives
+	SrcMod string // GOPATH/src/mod directory where versioned cache lives
 
 	CmdModInit   bool   // go mod -init flag
 	CmdModModule string // go mod -module flag