Fix default value supplied for cli configure

select_choice() expect to see only "tag" as default, not ("tag", "value") tuple

Closes: #605

dexbot/strategies/config_parts/relative_config.py

@@ -30,7 +30,7 @@ def configure(cls, return_base_config=True):
         relative_orders_config = [
             ConfigElement('external_feed', 'bool', False, 'External price feed',
                           'Use external reference price instead of center price acquired from the market', None),
-            ConfigElement('external_price_source', 'choice', EXCHANGES[0], 'External price source',
+            ConfigElement('external_price_source', 'choice', EXCHANGES[0][0], 'External price source',
                           'The bot will try to get price information from this source', EXCHANGES),
             ConfigElement('amount', 'float', 1, 'Amount',
                           'Fixed order size, expressed in quote asset, unless "relative order size" selected',