Allow user to update testdata files with parameter --refresh-pairs-cached (#174)

freqtrade/misc.py

@@ -166,6 +166,13 @@ def build_subcommands(parser: argparse.ArgumentParser) -> None:
         action='store_true',
         dest='realistic_simulation',
     )
+    backtesting_cmd.add_argument(
+        '-r', '--refresh-pairs-cached',
+        help='refresh the pairs files in tests/testdata with the latest data from Bittrex. Use it if you want to \
+              run your backtesting with up-to-date data.',
+        action='store_true',
+        dest='refresh_pairs',
+    )
 
     # Add hyperopt subcommand
     hyperopt_cmd = subparsers.add_parser('hyperopt', help='hyperopt module')