Changed maven deprecated method to new one

- Working without warnings on maven 3.1 and java 1.7.0_45


Before emmited warning on compile:
[INFO] Applying mojo extractor for language: java
[WARNING] pl.project13.maven.git.GitCommitIdMojo#project:
[WARNING]   The syntax
[WARNING]     @parameter expression="${property}"
[WARNING]   is deprecated, please use
[WARNING]     @parameter property="property"
[WARNING]   instead.
[WARNING] pl.project13.maven.git.GitCommitIdMojo#reactorProjects:
[WARNING]   The syntax
[WARNING]     @parameter expression="${property}"
[WARNING]   is deprecated, please use
[WARNING]     @parameter property="property"
[WARNING]   instead.
[WARNING] pl.project13.maven.git.GitCommitIdMojo#skipPoms:
[WARNING]   The syntax
[WARNING]     @parameter expression="${property}"
[WARNING]   is deprecated, please use
[WARNING]     @parameter property="property"
[WARNING]   instead.