Sort platform names in output file name

intercal/main.py

@@ -88,9 +88,10 @@ def unix_time(t):
 
 def output_file_name(args):
 
+    platform_1, platform_2 = sorted([args.platform_1, args.platform_2])
     earlier_time = min(args.time_1, args.time_2)
-    return 'sno_{}_{}_{}_{}.h5'.format(platform_tag(args.platform_1).lower(),
-                                       platform_tag(args.platform_2).lower(),
+    return 'sno_{}_{}_{}_{}.h5'.format(platform_tag(platform_1).lower(),
+                                       platform_tag(platform_2).lower(),
                                        args.sensor.lower(),
                                        earlier_time.strftime('%Y-%m-%dT%H-%M'))