Fix agentkeepalive version to 0.2.2

The latest agentkeepalive version (1.0.0) only works with node v0.11+.
Change package.json to pull version 0.2.2 as it is the last version to
support node v0.10.
Merge pull request #24 from get-the-service/agentkeepalive_version_fix

Fix agentkeepalive version to 0.2.2