DOC: Updating versions in the version switcher

Author: greglucas

docs/source/_static/version_switch.js

@@ -5,7 +5,8 @@
   'use strict';
 
   var all_versions = {
-    'latest': '0.18',
+    'latest': '0.19',
+    'v0.18': '0.18',
     'v0.17': '0.17',
     'v0.16': '0.16',
     'v0.15': '0.15',