getContext function is not compatible with Android API 21 or 22

[HazAnwar]

The use of getContext in the MainFragment.java doesn't work on older Fire TV devices such as Fire Stick 2nd Gen as it runs on API 22. getContext requires a minimum of API 23 to work, despite the minimum targeted API of this project being 21.

I would recommend replacing it with getActivity().getApplicationContext() instead as that works on my Fire Stick 2nd Gen running Fire OS 5.2.8.7 and essentially does the same thing.

I attempted to raise the PR myself but didn't have the correct rights to do so 😅