A trailing slash on --exclude (e.g. './lib/') is dropped during pattern
normalization but doublestar.Match still requires an exact string match,
so the resulting pattern silently matches nothing and the directory is
not excluded. Strip a trailing slash so './lib/' and './lib' behave the
same.
Fixes#4839
Signed-off-by: ChrisJr404 <chris@hacknow.com>
