Consider using jgit or similar instead of executing external process

[pzygielo]

glassfish-copyright-plugin/src/main/java/org/glassfish/copyright/AbstractCopyright.java

Lines 917 to 918 in 50f4d7a

	ProcessBuilder pb = new ProcessBuilder("git", "log", "-n", "1",
	"--decorate", "--date=local", file);

It might happen for this plugin to work on git cloned repository with no git available in $PATH. (Like in eclipse-ee4j/glassfish-build-maven-plugin#18).