go/gcexportdata: fix unnecessary plural type definitions of arg

importPath and srcDir are both of string type.

Change-Id: Ia5230bd19ea83bc210cb0b1a50046e4e0ef2accb
Reviewed-on: https://go-review.googlesource.com/42890
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: zchee

go/gcexportdata/gcexportdata.go

@@ -44,7 +44,7 @@ import (
 //
 // Find also returns the package's resolved (canonical) import path,
 // reflecting the effects of srcDir and vendoring on importPath.
-func Find(importPath string, srcDir string) (filename, path string) {
+func Find(importPath, srcDir string) (filename, path string) {
 	return gcimporter.FindPkg(importPath, srcDir)
 }