Update BuildInfoMojo.java

Removes the need to have spiffyui present in the project where this mojo is used.

If the spiffyui dependency is missing, the label "n/a" will be used instead of the version.

I also noted the dependency on the rev-info mojo in the javadoc for the type.
Merge pull request #5 from lji/master

Use SafeHTMLUtils.htmlEscape for title to prevent XSS issue