Merge pull request #32 from ryotashiraishi/topic_improv_design

Topic improv design
ランダム選択の実装とミッション一覧のレスポンシブデザインを微調整
ランダム選択時のパラメータ渡し誤りを修正
Merge remote-tracking branch 'origin/master' into topic_improv_design

Conflicts:
	app/views/missions/index.html.erb
	app/views/missions/show.html.erb