fixed spacing issue in docstring

Author: mirober

pandas/io/excel/_base.py

@@ -673,7 +673,7 @@ class ExcelWriter(metaclass=abc.ABCMeta):
             * new_sheet: Create a new sheet with a different name.
             * overwrite_sheet: Delete the contents of the sheet, then write to it.
             * overwrite_cells: Write directly to the named sheet
-            without deleting the previous contents.
+              without deleting the previous contents.
 
         .. versionadded:: 1.3.0