MAINT: Sort input file list

so that mumble_flags.qrc builds in a reproducible way
in spite of non-deterministic filesystem readdir order

See https://reproducible-builds.org/ for why this is good.

scripts/generate_flag_qrc.py

@@ -39,7 +39,7 @@ def main():
     # Get a list of all flag SVGs
     flags = []
 
-    for fn in os.listdir(args.flag_dir):
+    for fn in sorted(os.listdir(args.flag_dir)):
         if not fn.lower().endswith('svg'):
             continue