Resolve "negative center lat/lons (meso) confuse the parser"

Closes #22

gridded_glm/libexec/_minute_gridder.py

@@ -87,7 +87,7 @@ def create_parser():
                         type=float, help='center latitude (required for meso)')
     parser.add_argument('--ctr-lon', metavar='longitude',
                         type=float, help='center longitude (required for meso)')
-    parser.add_argument('-1', "--realtime", default=False, action='store_true',
+    parser.add_argument('-r', "--realtime", default=False, action='store_true',
                         help="enable 'realtime' mode, where we expect only one input file,\n"
                         "find the surrounding trio, and automatically determine if a full minute\n"
                         "of data is available (default: off)")