Remove GitHub buttons from social_buttons partial
Remove GitHub buttons from social_buttons partial

Most of readers who visited this website don't know GitHub.
It may be confising, so temporarily remove the button.

coderdojo-japan/coderdojo.jp,coderdojo-japan/coderdojo.jp,yasslab/coderdojo.jp,coderdojo-japan/coderdojo.jp,yasslab/coderdojo.jp,yasslab/coderdojo.jp,coderdojo-japan/coderdojo.jp