test: Install missing dev dependency for linting

[paulmelnikow]

Without this change:

> nock@0.0.0-development pretest /Users/pnm/code/nock
> npm run -s lint

internal/modules/cjs/loader.js:582
    throw err;
    ^

Error: Cannot find module 'acorn'
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:580:15)
    at Function.Module._load (internal/modules/cjs/loader.js:506:25)
    at Module.require (internal/modules/cjs/loader.js:636:17)
    at require (internal/modules/cjs/helpers.js:20:18)
    at Object.<anonymous> (/Users/pnm/code/nock/node_modules/acorn-jsx/index.js:8:15)
    at Module._compile (internal/modules/cjs/loader.js:688:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:699:10)
    at Module.load (internal/modules/cjs/loader.js:598:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:537:12)
    at Function.Module._load (internal/modules/cjs/loader.js:529:3)

[RichardLitt]

Thanks @paulmelnikow.

[nockbot]

🎉 This PR is included in version 11.0.0-beta.1 🎉

The release is available on:

• npm package (@beta dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[nockbot]

🎉 This PR is included in version 10.0.5 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue and add a reference to this one if it’s related. Thank you!

[nockbot]

🎉 This PR is included in version 11.0.0 🎉

The release is available on:

• npm package (@next dist-tag)
• GitHub release

Your semantic-release bot 📦🚀