Fix inconsistant lemmatizer issue #3484 (#3646)

* Fix inconsistant lemmatizer issue #3484

* Remove test case

spacy/lemmatizer.py

@@ -1,5 +1,6 @@
 # coding: utf8
 from __future__ import unicode_literals
+from collections import OrderedDict
 
 from .symbols import POS, NOUN, VERB, ADJ, PUNCT, PROPN
 from .symbols import VerbForm_inf, VerbForm_none, Number_sing, Degree_pos
@@ -118,8 +119,8 @@ def lemmatize(string, index, exceptions, rules):
  forms.append(form)
  else:
  oov_forms.append(form)
- # Remove duplicates, and sort forms generated by rules alphabetically.
- forms = list(set(forms))
+ # Remove duplicates but preserve the ordering of applied "rules"
+ forms = list(OrderedDict.fromkeys(forms))
  # Put exceptions at the front of the list, so they get priority.
  # This is a dodgy heuristic -- but it's the best we can do until we get
  # frequencies on this. We can at least prune out problematic exceptions,