do not suppose that GOPATH is added to PATH

```
brew install tendermint --HEAD
==> Installing tendermint from tendermint/tendermint
==> Cloning https://github.com/tendermint/tendermint.git
Cloning into '/Users/antonk/Library/Caches/Homebrew/tendermint--git'...
remote: Counting objects: 437, done.
remote: Compressing objects: 100% (412/412), done.
remote: Total 437 (delta 7), reused 129 (delta 2), pack-reused 0
Receiving objects: 100% (437/437), 3.04 MiB | 1006.00 KiB/s, done.
Resolving deltas: 100% (7/7), done.
==> Checking out branch develop
==> make get_vendor_deps
Last 15 lines from /Users/antonk/Library/Logs/Homebrew/tendermint/01.make:
2017-12-04 14:54:54 -0600

make
get_vendor_deps

go get github.com/mitchellh/gox github.com/tcnksm/ghr github.com/Masterminds/glide github.com/alecthomas/gometalinter
make: gometalinter: No such file or directory
make: *** [ensure_tools] Error 1

If reporting this issue please do so at (not Homebrew/brew or Homebrew/core):
https://github.com/tendermint/homebrew-tendermint/issues
```

Makefile

@@ -79,7 +79,7 @@ tools:
 
 ensure_tools:
 	go get $(GOTOOLS)
-	@gometalinter --install
+	test -f gometalinter & gometalinter --install
 
 ### Formatting, linting, and vetting