adicionado imagens no usuario github e gravatar no profile
Merge branch 'github-image' of github.com:mfbmina/RubyCastsBrasil into github-image

Conflicts:
	CONTRIBUTORS.md
	app/assets/stylesheets/application.scss
	app/models/profile.rb
	db/schema.rb
	spec/models/profile_spec.rb
Merge pull request #164 from mfbmina/github-image

Adicionado imagens do gravatar e github