Bugfix (abhijithneilabraham#56)

* Update data_utils.py

* Update .travis.yml

* Update nlp.py

* Update nlp.py

Author: abhijithneilabraham

tableqa/nlp.py

@@ -342,7 +342,7 @@ def get_sql_query(self,df,q,distinct):
             unknown_slots=unknown_slots['main_slot']
         else:
            unknown_slots= ','.join(unknown_slots['slots'])
-        if unknown_slots is None:
+        if not(unknown_slots and unknown_slots.strip()):
             unknown_slots='*'
         question=question.format(unknown_slots,schema["name"].lower())