Move bn-BD to bn (Bengali)

config.js

@@ -4,7 +4,7 @@ module.exports = {
     'ar',
     'ast',
     'bg',
-    'bn-BD',
+    'bn',
     'bs',
     'ca',
     'cak',

locale/bn/LC_MESSAGES/messages.po

@@ -7,7 +7,7 @@ msgstr ""
 "PO-Revision-Date: 2018-02-01 21:30+0000\n"
 "Last-Translator: S M Sarwar Nobin <smsarwar1996@gmail.com>\n"
 "Language-Team: none\n"
-"Language: bn_BD\n"
+"Language: bn\n"
 "MIME-Version: 1.0\n"
 "Content-Type: text/plain; charset=UTF-8\n"
 "Content-Transfer-Encoding: 8bit\n"