Correct version in podspec

[fiznool]

Sets the version defined by the podspec according to that in package.json.

I don't know very much about cocoapods but might this be a fix for #82? Surely it can't be this simple though 😄

[koenpunt]

Something like this was what I intended for #82, but there’s a syntax error

[reimertz]

First, thanks @naoufal and contributors for all the hard work, secondly, any reason we don't merge this?