Replace num_words to topn in LdaMallet.show_topics. Fix #1747 (#1749)

Author: apoorvaeternity

gensim/models/wrappers/ldamallet.py

@@ -258,7 +258,7 @@ def show_topics(self, num_topics=10, num_words=10, log=False, formatted=True):
             if formatted:
                 topic = self.print_topic(i, topn=num_words)
             else:
-                topic = self.show_topic(i, num_words=num_words)
+                topic = self.show_topic(i, topn=num_words)
             shown.append((i, topic))
             if log:
                 logger.info("topic #%i (%.3f): %s", i, self.alpha[i], topic)