[2905] require.context importing ignored files

This is related, and noted in PR #2594. There was no issue created, so I figured I would document this.

Currently I have a store folder that holds my modules. It has an index.js file that exports the store creation function. I also keep tests next to the files in the form of module.integration.js or module.spec.js. Currently nuxt tries to import these tests files (even though they are ignored), which causes a huge amount of webpack errors.

 ERROR  Failed to compile with 22 errors                                                                                                               14:08:26

These dependencies were not found:

* child_process in ./node_modules/jsdom/lib/jsdom/living/xmlhttprequest.js
* fs in ./node_modules/ava/lib/snapshot-manager.js, ./node_modules/ava/lib/process-adapter.js and 12 others
* module in ./node_modules/require-extension-hooks/src/index.js, ./node_modules/time-require/src/requireHook.js
* net in ./node_modules/forever-agent/index.js, ./node_modules/tough-cookie/lib/cookie.js and 1 other
* tls in ./node_modules/forever-agent/index.js, ./node_modules/tunnel-agent/index.js

Relevent code line: https://github.com/nuxt/nuxt.js/blob/dev/lib/app/store.js#L7