refine go tools script

Author: ccsexyz

install_go_tools.sh

@@ -12,5 +12,10 @@ go get -u -v github.com/zmb3/goaddimport
 go get -u -v github.com/rogpeppe/godef
 go get -u -v golang.org/x/tools/cmd/guru
 go get -u -v github.com/fatih/gomodifytags
-go get -u -v github.com/tpng/gopkgs
+if [ `uname` == "Darwin" ]
+then
+    go get -u -v github.com/uudashr/gopkgs/cmd/gopkgs
+else
+    go get -u -v github.com/tpng/gopkgs
+fi
 go get -u -v github.com/ramya-rao-a/go-outline