Change import path for Go tools to new path.

The Go tools repository has been moved: https://groups.google.com/d/msg/golang-nuts/eD8dh3T9yyA/l5Ail-xfMiAJ
Proposing that the paths are updated here as well.
Merge pull request #90 from hansrodtang/patch-1

Change import path for Go tools to new golang.org/x/ path.