Convert ExecutePendingTransactions to CommitNow
As per this StackOverflow post, I am receiving [this error](https://stackoverflow.com/questions/38722325/fragmentmanager-is-already-executing-transactions-when-is-it-safe-to-initialise), and the solution for it is to convert ExecutePendingTransactions to CommitNow instead after SDK 24.

I noticed that we are still using ExecutePendingTransactions in [this file]( https://github.com/MvvmCross/MvvmCross/blob/5354b207f2f626035a631b3762642ebdc3b48172/MvvmCross/Platforms/Android/Views/MvxTabsFragmentActivity.cs#L192), and was wondering if I could go ahead and change this for the next release?

Please let me know if I can make that change and against what branch, and I will submit a PR for it.