Update ruby-xmpp4r to 0.5.6.

xmpp4r 0.5.6 (February 14th, 2013)
====================================

* [DOC] Wrong inline documentation in `client.rb`; details of port number
  parameter and removal of un-used 'use_ssl parameter'
* Prevent REXML exceptions on UTF-8 messages
* Fixed broken parse method
* Make sure to open files in binary mode, in order to correctly transfer
  files on Windows
* Prevent REXML exceptions on UTF-8 messages
* Better control of history on muc.join


xmpp4r 0.5.5 (October 6th, 2013)
===============================
* Removed unnecessary dependency on pry.

* Merge pull request #1 from Strech/patch-1
  * Non-bosh connection flushes correctly
* Elaborated debug messages in HTTPBinding::Client

* Modified to work with BOSH with HTTPBinding::Client
  - Support stream restart with urn:xmpp:xbosh way.
  - Removed unnecessary wait until authenticated.
  - Added Semaphore to wait for auth and bind response.
  - Hook to setup SSL flags (certificate, etc.)
  - Adjusted HTTP::Net read_timeout according to http_wait.
  - Proxy handling.
  - Respect poll/request BOSH parameters to avoid overactivity.
Remove stale entry
Update mongodb to 2.6.1.

Notable changes since 2.6.0:
- Fix to install MongoDB service on Windows with the --install option
- Allow direct upgrade from 2.4.x to 2.6.0 via yum
- Fix issues with background index builds on secondaries
- Redact credential information passed as startup options

See full changelog:

http://docs.mongodb.org/manual/release-notes/2.6-changelog/