Fix Gradle Maven repository and Groovy dependency syntax.
Bump Groovy version to 1.8.8 (latest stable in 1.8.x: 1.8.7 is required for collectEntries() in the following) and Spock version to 0.7.
Bump OpenCSV version to 2.3.
Adds toMap() to PropertyMapper. Fixes #25.
Ensures that the keys are ordered according to their associated value.
Merge pull request #28 from gmazelier/issue25

Closes #25. Thanks!