minor beautification

Author: Thomas Lautenschlaeger

pandas/core/frame.py

@@ -9224,7 +9224,7 @@ def _gotitem(
     Works equivalently as above. Add argument `numeric_only=True` to
     aggregate only numeric columns.
 
-    >>> df.agg({'B': ["mean", 'std'], 'C': ['sum', 'mean']},
+    >>> df.agg({'B': ['mean', 'std'], 'C': ['sum', 'mean']},
     ...                    numeric_only=True)
             B     C
     mean  2.0   5.0