TST: Fix unprintable message when skipping (#362)

Ensure string version of message is printed when skipping a test

Author: bashtage

pandas_datareader/_testing.py

@@ -25,7 +25,7 @@ def wrapper(*args, **kwargs):
             try:
                 f(*args, **kwargs)
             except exp as e:
-                skip(e)
+                skip(str(e))
 
         return wrapper