Fix greedy regex in dh-exec-install-rename

When encountering lines like "foo  => bar", dh-exec-install-rename ends up
taking "foo " as $src instead of "foo", resulting in an ENOENT. This commit
fixes it by disallowing \s inside the regex groups for $src and $dst.
Merge pull request #1 from hyperair/master

Fix greedy regex in dh-exec-install-rename