Normalize beam speed
Use cc.pSub
Merge pull request #29 from soltycabbage/feature/beam_speed

ビームの速度計算に単位ベクトルを用いることでビームの速度を一定にした
Merge branch 'master' into mob-beam-ataru-ore-tuyoi

Conflicts:
	public/js/src/entity/beam.js