fixed typo in isMapRotationEnabled

I noticed that MapView had a method named istMapRotationEnabled, which I assume is a typo. I changed it to isMapRotationEnabled in the MapView class, as well as the docs. If this is indeed a typo, please consider merging my branch. This is my first time submitting a pull request, so if I have the wrong branch or anything, please let me know and I will gladly fix it. Thanks.