Improve the exception message of UrlMatcher

The current exception message is not optimal, some more context always helps.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT
you should use single quotes i believe to make it consistent with other parts of the code?