Update Podspec for Swift 4.2

[ugenlik]

for swift 4.2
pod 'TransitionButton', :git => 'https://github.com/AladinWay/TransitionButton.git' works

but just pod 'TransitionButton' doesn't work it pulls the last version not the master branch of the repo.

[AladinWay]

I have just released the version 0.5.2 so it should be fine now to use just pod 'TransitionButton' make sure to run pod repo update first