Fix changelog entry date format

assets/javascripts/news.json

@@ -1,6 +1,6 @@
 [
   [
-    "2018-2-4",
+    "2018-02-04",
     "New documentations: <a href=\"/babel/\">Babel</a>, <a href=\"/jekyll/\">Jekyll</a> and <a href=\"/jsdoc/\">JSDoc</a>"
   ], [
     "2017-11-26",