Crude fix on line 79 to enforce no out of bounds error

umbra/mistake_finder.py

@@ -76,7 +76,7 @@ class MistakeFinder:
             src_index = self._source.index(
                 self._shadow[shd_anchor_index].anchor)
         while self._source[src_index].get_difference(shd_word) > 0 and\
-                not semantic_mistake:
+                not semantic_mistake and src_index < (len(self._source)-1): # Crude fix, but removes error
             src_word = self._source[src_index]
             if self.semantically_related(src_word, shd_word):
                 shd_word.mistake = Mistake.SEMANTIC