Fix bind2 namespace

XEP-0386 defines it as `urn:xmpp:bind:0`:
https://xmpp.org/extensions/xep-0386.html#sect-idm45625558119104

Author: mdosch

xep-0515.xml

@@ -120,7 +120,7 @@
       <!-- Server indicates that XEP-0198 can be negotiated "inline" -->
       <enable xmlns='urn:xmpp:sm:3'/>
       <!-- Server indicates support for XEP-0386 Bind 2 -->
-      <bind xmlns='urn:xmpp:bind2:1'/>
+      <bind xmlns='urn:xmpp:bind:0'/>
     </inline>
   </authentication>
   <!-- Channel-binding information provided by XEP-0440 -->