Update ruby-cassandra to 0.22.0.

v0.22.0
- Add new composite API to resolve ambiguity between unpacking a composite and packing a composite with one element (issue #196, courtesy @kevinkehl)
- Breaking change: schema change methods no longer catch exceptions internally.  They work the same as everything else.

v0.21.0
- Add 1.2 libs to gem

v0.19.0
- Fixed windows build by disabling native extensions (issue #188, courtesy @jacek99)
- Speed improvement to native composite column extension (issue #186, courtesy @muirmanders)
- Fix OrderedHash iterator return values (issue #185, courtesy @fester)
- Native support for dynamic composite decoding (issue #184, courtesy @muirmanders)

v0.18.0
- Cassandra 1.2 support (issue #175, courtesy @brainopia)
- drop_keyspace defaults to current keyspace (issue #176, courtesy @brianopia)
- Easier flush_batch interface (issue #182, courtesy @brianopia)
- Support for removing multiple columns (issue #183, courtesy @brianopia)

(taca)