Fix positional params used for gensim.models.CoherenceModel in `gen…

…sim.models.callbacks` (piskvorky#1823)

* add keyword params for call to gensim.models.CoherenceModel as positional arguments for coherence and topn were incorrect due to skipping param for keyed_vectors

* Fix PEP8

gensim/models/callbacks.py

@@ -98,10 +98,13 @@ def get_value(self, **kwargs):
         self.model = None
         self.topics = None
         super(CoherenceMetric, self).set_parameters(**kwargs)
+
         cm = gensim.models.CoherenceModel(
-            self.model, self.topics, self.texts, self.corpus, self.dictionary,
-            self.window_size, self.coherence, self.topn
+            model=self.model, topics=self.topics, texts=self.texts, corpus=self.corpus,
+            dictionary=self.dictionary, window_size=self.window_size,
+            coherence=self.coherence, topn=self.topn
         )
+
         return cm.get_coherence()