(기타) gitignore 변경

merge confliction을 방지하기 위하여 .gitignore에 *.dex, *.ap_, *.apk, *.cache를
추가하였다.
Merge remote-tracking branch 'origin/pjhjohn' into Y
Merge remote-tracking branch 'origin/pjhjohn' into Y
[Appending] bubble.Unit

added source on unit of bubble game
[Merging] No need to check it