Update module gorilla/mux to v1.7.4

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
github.com/gorilla/mux	require	patch	v1.7.3 -> v1.7.4

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Release Notes

gorilla/mux

### [`v1.7.4`](https://togithub.com/gorilla/mux/releases/v1.7.4) [Compare Source](https://togithub.com/gorilla/mux/compare/v1.7.3...v1.7.4) v1.7.4 addresses a number of performance improvements ([#​544](https://togithub.com/gorilla/mux/issues/544)), bugs ([#​509](https://togithub.com/gorilla/mux/issues/509), [#​535](https://togithub.com/gorilla/mux/issues/535)), and documentation improvements. #### CHANGELOG - Reduce allocations in (\*routeRegexp).getURLQuery ([#​544](https://togithub.com/gorilla/mux/issues/544)) [@​klauspost](https://togithub.com/klauspost) - Fixed golint warnings ([#​526](https://togithub.com/gorilla/mux/issues/526)) [@​KosToZyB](https://togithub.com/KosToZyB) - fix headers regexp test case ([#​536](https://togithub.com/gorilla/mux/issues/536)) [@​icattlecoder](https://togithub.com/icattlecoder) - Fix the CORSMethodMiddleware bug with subrouters ([#​535](https://togithub.com/gorilla/mux/issues/535)) [@​fharding1](https://togithub.com/fharding1) - Remove/cleanup request context helpers ([#​525](https://togithub.com/gorilla/mux/issues/525)) [@​fharding1](https://togithub.com/fharding1) - Guess the scheme if r.URL.Scheme is unset ([#​474](https://togithub.com/gorilla/mux/issues/474)) [@​euank](https://togithub.com/euank) - Added capacity to slice creation, when capacity is known ([#​516](https://togithub.com/gorilla/mux/issues/516)) [@​vivekv96](https://togithub.com/vivekv96) - Modified http status codes, using constants provided by the http package ([#​514](https://togithub.com/gorilla/mux/issues/514)) [@​vivekv96](https://togithub.com/vivekv96) - bugfix/subrouter custom methodNotAllowed handler returning 404 ([#​509](https://togithub.com/gorilla/mux/issues/509)) ([#​510](https://togithub.com/gorilla/mux/issues/510)) [@​jonasdebeukelaer](https://togithub.com/jonasdebeukelaer) - Update README (self-host logo) ([#​513](https://togithub.com/gorilla/mux/issues/513)) [@​elithrar](https://togithub.com/elithrar) - Remove TravisCI badge ([#​503](https://togithub.com/gorilla/mux/issues/503)) [@​elithrar](https://togithub.com/elithrar) - Add documentation for using mux to serve a SPA ([#​493](https://togithub.com/gorilla/mux/issues/493)) [@​fharding1](https://togithub.com/fharding1) - Simplify code ([#​501](https://togithub.com/gorilla/mux/issues/501)) [@​muesli](https://togithub.com/muesli) - Avoid unnecessary conversion ([#​502](https://togithub.com/gorilla/mux/issues/502)) [@​muesli](https://togithub.com/muesli) - Update config.yml ([#​495](https://togithub.com/gorilla/mux/issues/495)) [@​elithrar](https://togithub.com/elithrar)

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