Bump koa from 2.4.1 to 2.5.1

[dependabot-preview]

Bumps koa from 2.4.1 to 2.5.1.

Changelog

Sourced from koa's changelog.

2.5.1 / 2018-04-27

• test: node v10 on travis (#1182)
• fix tests: remove unnecessary assert doesNotThrow and api calls (#1170)
• use this.response insteadof this.ctx.response (#1163)
• deps: remove istanbul (#1151)
• Update guide.md (#1150)

2.5.0 / 2018-02-11

• feat: ignore set header/status when header sent (#1137)
• run coverage using --runInBand (#1141)
• [Update] license year to 2018 (#1130)
• docs: small grammatical fix in api docs index (#1111)
• docs: fixed typo (#1112)
• docs: capitalize K in word koa (#1126)
• Error handling: on non-error throw try to stringify if error is an object (#1113)
• Use eslint-config-koa (#1105)
• Update mgol's name in AUTHORS, add .mailmap (#1100)
• Avoid generating package locks instead of ignoring them (#1108)
• chore: update copyright year to 2017 (#1095)

Commits

• 45464b5 Release 2.5.1
• 2ace704 test: node v10 on travis (#1182)
• 13086d2 fix tests: remove unnecessary assert doesNotThrow and api calls (#1170)
• 8c17517 use this.response insteadof this.ctx.response (#1163)
• 9cef2db deps: remove istanbul (#1151)
• 0698d67 Update guide.md (#1150)
• 916f914 Release 2.5.0
• 3c23aa5 feat: ignore set header/status when header sent (#1137)
• 0923ef6 run coverage using --runInBand (#1141)
• e544012 [Update] license year to 2018 (#1130)
• Additional commits viewable in compare view

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