BRK: Rename stats._trades key 'Commissions' -> 'Commission'

The word is long enough as it is.
I tried to monkey-wrap it with a deprecation warning,
but couldn't figure it out pandas-wise.

Author: kernc

backtesting/_stats.py

@@ -67,7 +67,7 @@ def compute_stats(
             'SL': [t.sl for t in trades],
             'TP': [t.tp for t in trades],
             'PnL': [t.pl for t in trades],
-            'Commissions': [t._commissions for t in trades],
+            'Commission': [t._commissions for t in trades],
             'ReturnPct': [t.pl_pct for t in trades],
             'EntryTime': [t.entry_time for t in trades],
             'ExitTime': [t.exit_time for t in trades],

backtesting/test/_test.py

@@ -347,7 +347,7 @@ def almost_equal(a, b):
             sorted(stats['_trades'].columns),
             sorted(['Size', 'EntryBar', 'ExitBar', 'EntryPrice', 'ExitPrice',
                     'SL', 'TP', 'PnL', 'ReturnPct', 'EntryTime', 'ExitTime',
-                    'Duration', 'Tag', 'Commissions',
+                    'Duration', 'Tag', 'Commission',
                     *indicator_columns]))
 
     def test_compute_stats_bordercase(self):