Add github.com/pkg/errors to .travis.yml

Author: Damir Vandic

.travis.yml

@@ -13,6 +13,7 @@ matrix:
 before_install:
   - go get github.com/axw/gocov/gocov
   - go get github.com/mattn/goveralls
+  - go get github.com/pkg/errors
 
 script:
   - $HOME/gopath/bin/goveralls -service=travis-ci