Bump mojo-executor dep to 2.2.0 for maven 3.1 compatibility.

Tested with:
```
$ mvn -v
Apache Maven 3.1.1 (NON-CANONICAL_2013-10-11_13-55_root; 2013-10-11 11:55:32+0200)
Maven home: /opt/maven
Java version: 1.7.0_45, vendor: Oracle Corporation
Java home: /opt/java/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "3.12.2-1-arch", arch: "amd64", family: "unix"
```
I also attached a `.gitignore` with a rule to ignore `/target` dir.