Lemmatization of Adjectives - French : adding rules and vocabulary (#3045)

* modifying FR lemmatisation for Adjectives

* adding contributor agreement for amperinet

* correcting some errors in vocabulary files

.github/contributors/amperinet.md

@@ -101,6 +101,6 @@ mark both statements:
 | Name                           | Amandine Périnet        |
 | Company name (if applicable)   | 365Talents              |
 | Title or role (if applicable)  | Data Science Researcher |
-| Date                           | 04/12/2018              |
+| Date                           | 12/12/2018              |
 | GitHub username                | amperinet               |
 | Website (optional)             |                         |

spacy/lang/fr/lemmatizer/_lemma_rules.py

@@ -3,9 +3,26 @@ from __future__ import unicode_literals
 
 
 ADJECTIVE_RULES = [
-    ["s", ""],
+    ["a", "a"],
+    ["aux", "al"],
+    ["c", "c"],
+    ["d", "d"],
     ["e", ""],
-    ["es", ""] 
+    ["é", "é"],
+    ["eux", "eux"],
+    ["f", "f"],
+    ["i", "i"],
+    ["ï", "ï"],
+    ["l", "l"],
+    ["m", "m"],
+    ["n", "n"],
+    ["o", "o"],
+    ["p", "p"],
+    ["r", "r"],
+    ["s", ""],
+    ["t", "t"],
+    ["u", "u"],
+    ["y", "y"]
 ]