Remove hardcoded tower cost value
Remove hardcoded tower cost value

garysheng/tower-defense-game-engine,dianwen/oogasalad_TowerDefense,codylieu/oogasalad_OOGALoompas,jordanly/oogasalad_OOGALoompas,dennis-park/OOGALoompas,sdh31/tower_defense,kevinkdo/oogasalad_OOGALoompas