Fix #13: Make Irony-Ac works with any known YASnippet ATM

The following versions of YASnippet have been tested and work:
- 0.1.1
- 0.2.3
- 0.5.4
- 0.5.7
- 0.5.10
- 0.6.0b
- 0.6.0c
- 0.6.1b
- 0.6.1c
- 0.8.0 (beta)