Fix detection of deps dir for cover.spec files

It seems that collect_glob/3 does not correctly determine that it should skip a cover.spec file inside a dependency directory and it ends up seeing all available cover.spec files (the one for the root project and the ones inside their deps). The fix in this case is to try to detect cover.spec files that are inside the deps directory by trying to match the start of the absolute path against the deps directory in a simple way.