Branch is always UNKNOWN with git

Plugin tries to obtain branch from URL, which doesn't work with git.

Steps to reproduce:
1. Add the following section to a pom build in a git repository
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>buildnumber-maven-plugin</artifactId>
<version>1.1-SNAPSHOT</version>
<executions>
<execution>
<phase>validate</phase>
<goals>
<goal>create</goal>
</goals>
</execution>
</executions>
</plugin>
2. Look at build output - branch is always identified as UNKNOWN

Patch attached (works, but might be questionable - I'm definitely not a maven plugin expert).