Support for GD_GEM_USER, GD_GEM_PASSWORD
Mentioned possibility of GD_GEM_USER, GD_GEM_PASSWORD usage in CHANGELOG.md
Merge branch 'master' of https://github.com/gooddata/gooddata-ruby into gd-vars

Conflicts:
	CHANGELOG.md
Fix issues
Merge pull request #353 from korczis/gd-vars

Support for GD_GEM_USER, GD_GEM_PASSWORD