Upgrade path to regexp

[Sinewyk]

Upgrade path-to-regexp from 1.x to ^6.x

then:

• https://github.com/koajs/router/commit/ff31e4b355bbb732ffd87605542eb3d76986aa70 to fix tests only
• https://github.com/koajs/router/commit/78a292925594f6acb6def50723094467e7c2c413 to deal with path-to-regexp encode/decode being by default the identity function x => x ... send the options to compile and be explicit in the tests
• https://github.com/koajs/router/commit/5fcc2ed01a377fe935e0b540226ddc8ab11b53d3 be explicit in the router url tests
• https://github.com/koajs/router/commit/e047222f10a63dc9cf57815f9a2697772a44748b deal with the path-to-regexp@2.0 breaking change regarding explicit trailing slash handling https://github.com/pillarjs/path-to-regexp/blob/0c466b1b0944e8d0022b5b15069364a8483bf9c5/History.md#200--2017-08-23 ... I added tests, it should not be a breaking change for us because I added a specific behavior when path === '/' and prefix, we can target trailing slash by using the strict option.

should fixes #40

should be a straight upgrade over https://github.com/koajs/router/pull/70

Maybe breaking change (major semver) related to the encode/decode situation.

[niftylettuce]

v9.0.0 released to npm

https://github.com/koajs/router/releases/tag/v9.0.0

[niftylettuce]

Ping @Sinewyk @tigt -- can you resolve/PR?