fix extraneous backslash

Author: rforgione

pandas/util/validators.py

@@ -219,6 +219,6 @@ def validate_args_and_kwargs(fname, args, kwargs,
 def validate_bool_kwarg(value, arg_name):
     """ Ensures that argument passed in arg_name is of type bool. """
     if not (is_bool(value) or value is None):
-        raise ValueError('For argument "%s" expected type bool, ' % arg_name +\
+        raise ValueError('For argument "%s" expected type bool, ' % arg_name +
             'received type %s.' % type(value).__name__)
     return value