We just need jdk for this script that helps set up toolchains. The
script might need to know about the target platform, but the interpreter
that runs it (or part of it) doesn't.
Move to a known version of the emulator. Each OS has a distinct
version... pick the one on Linux. A better solution would be to let
the user of `emulateApp` overload what the emulator version shall be
(and maybe it is already possible and I do not see it) - without need
to reproduce large portions of `default.nix`.
Using the previous emulator showed the following warning:
```
Your emulator is out of date, please update by launching Android Studio:
```
I am not aware of any reasons for not wanting the latest emulator (as
I expect it shall be compatible usually with more system images - not
less), so bump its default version.
Emulator release notes:
https://developer.android.com/studio/releases/emulator
