Add Deptrac to Static Analysis (#1022)

README.md

 *Libraries for performing static analysis of PHP code.*
 
 * [Exakat](https://github.com/exakat/exakat) - A static analysis engine for PHP.
+* [Deptrac](https://github.com/sensiolabs-de/deptrac) - A static code analysis tool that helps to enforce rules for dependencies between software layers.
 * [Mondrian](https://github.com/Trismegiste/Mondrian) - A code analysis tool using Graph Theory.
 * [phan](https://github.com/phan/phan) - A static analyzer based on PHP 7+ and the php-ast extension.
 * [PHPCompatibility](https://github.com/PHPCompatibility/PHPCompatibility) - A PHP compatibility checker for PHP CodeSniffer.