ballz: rename FDroid metadata file

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/examples/mnit_ballz/org.nitlanguage.ballz_android.txt b/examples/mnit_ballz/org.nitlanguage.ballz.txt
similarity index 100%
rename from examples/mnit_ballz/org.nitlanguage.ballz_android.txt
rename to examples/mnit_ballz/org.nitlanguage.ballz.txt