Bump xmpp-parsers to 0.12.2.

This also removes minidom, jid and try_from as direct dependencies,
since they are now reexported by xmpp-parsers.

src/xmpp_codec.rs

@@ -2,7 +2,7 @@
 
 use crate::{ParseError, ParserError};
 use bytes::{BufMut, BytesMut};
-use minidom::Element;
+use xmpp_parsers::Element;
 use quick_xml::Writer as EventWriter;
 use std;
 use std::cell::RefCell;