Fix pep8

Author: bsipocz

astroquery/esa/hubble/tests/test_esa_hubble.py

@@ -444,4 +444,4 @@ def test_empty_list(self):
                                 output_format="votable",
                                 verbose=True)
         assert "One of the lists is empty or there are "\
-               "elements that are not strings" in err.value.args[0]
+               "elements that are not strings" in err.value.args[0]