Fix /lib/ ignore ruleset

[Rud5G]

See #81 , the expected behaviour is: ignoring the '/lib/* directory the relative path is matched without the starting directory separator. see https://github.com/squizlabs/PHP_CodeSniffer/blob/master/src/Filters/Filter.php#L221 hence the removal of the starting /

[lenaorobei]

@Rud5G thank you fo the contribution!