Fix native library version in FBReader 2.5.9
Fix native library version in FBReader 2.5.9

Was being built with a native library only compatible with android-21
and above.  Since the min supported version should be android-11, added
a command to prebuild to force android-11 in the jni.

f-droid/fdroid-data,f-droid/fdroiddata,f-droid/fdroiddata