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
oops, I saw your message after merging this PR. I fixed the double-quotes in df244f2