use parentheses for multiline string instead of backslash

freqtrade/tests/test_backtesting.py

@@ -23,8 +23,8 @@ logger = logging.getLogger(__name__)
 
 
 def format_results(results: DataFrame):
-    return 'Made {} buys. Average profit {:.2f}%. ' \
-           'Total profit was {:.3f}. Average duration {:.1f} mins.'.format(
+    return ('Made {} buys. Average profit {:.2f}%. '
+            'Total profit was {:.3f}. Average duration {:.1f} mins.').format(
                 len(results.index),
                 results.profit.mean() * 100.0,
                 results.profit.sum(),