fix pep8

Author: charlesdong1991

pandas/core/strings.py

@@ -582,8 +582,8 @@ def str_replace(arr, pat, repl, n=-1, case=None, flags=0, regex=None):
         # in pat, still take it as a literal, and raise the Future warning
         if regex is None and len(pat) == 1 and re.findall(r"\W", pat):
             warnings.warn("'%s' is interpreted as a literal in " % pat +
-                          "default, not regex. It will change in the future."
-                          , FutureWarning)
+                          "default, not regex. It will change in the future.",
+                          FutureWarning)
         f = lambda x: x.replace(pat, repl, n)
 
     return _na_map(f, arr)