Update python/datafusion/dataframe.py

Co-authored-by: Hendrik Makait <hendrik@makait.com>

Author: milenkovicm

python/datafusion/dataframe.py

@@ -567,7 +567,7 @@ def with_columns(
 
         Args:
             exprs: Either a single expression, an iterable of expressions to add or
-                   string SQL expressions.
+                   SQL expression strings.
             named_exprs: Named expressions in the form of ``name=expr``
 
         Returns: