Add build path to phploc directory

I was getting told "No files found to scan" from the phploc plugin. Tried with a leading slash:

    RUNNING PLUGIN: php_loc
    Executing: /var/www/phpci/vendor/bin/phploc  --exclude /lib/vendor --exclude /lib/tests "/lib/src"
    phploc 2.0.6 by Sebastian Bergmann.

    No files found to scan

And without:

    RUNNING PLUGIN: php_loc
    Executing: /var/www/phpci/vendor/bin/phploc  --exclude /lib/vendor --exclude /lib/tests "lib/src"
    phploc 2.0.6 by Sebastian Bergmann.

    No files found to scan

This change has fixed it so I now get phploc output and a working LoC chart.  That said, the command line now has a double slash at the start, so I guess there's something else going on as well...

    RUNNING PLUGIN: php_loc
    Executing: /var/www/phpci/vendor/bin/phploc  --exclude /lib/vendor --exclude /lib/tests "//lib/src"
    phploc 2.0.6 by Sebastian Bergmann.

    Directories                                          8
    Files                                               17
    ...

Test output:

    chandisi@cam-ci:~/PHPCI$ phpunit
    PHPUnit 4.1.3 by Sebastian Bergmann.
    
    Configuration read from /home/chandisi/PHPCI/phpunit.xml
    
    ................................................................. 65 / 74 ( 87%)
    .........
    
    Time: 1.52 seconds, Memory: 12.25Mb
    
    OK (74 tests, 137 assertions)