Chore/align node support same as karma - fix current failing CI

[elpddev]

Reason

Current travisci builds are failing for:

1. node < 6, npm update of npm tries to install npm version 6 that does not support node <= 4.

9.74s$ npm install -g npm
/home/travis/.nvm/versions/node/v4.9.1/bin/npm -> /home/travis/.nvm/versions/node/v4.9.1/lib/node_modules/npm/bin/npm-cli.js
/home/travis/.nvm/versions/node/v4.9.1/bin/npx -> /home/travis/.nvm/versions/node/v4.9.1/lib/node_modules/npm/bin/npx-cli.js
npm@6.9.0 /home/travis/.nvm/versions/node/v4.9.1/lib/node_modules/npm
/home/travis/.nvm/versions/node/v4.9.1/lib/node_modules/npm/bin/npm-cli.js:84
      let notifier = require('update-notifier')({pkg})
      ^^^
SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode

2. node stable (12), mock-fs old version support node up until version 7 and emit support error.

$ npm run test:lib
> karma-mocha@1.3.0 test:lib /home/travis/build/karma-runner/karma-mocha
> mocha test/lib
/home/travis/build/karma-runner/karma-mocha/node_modules/mock-fs/lib/index.js:38
  throw new Error('Unsupported Node version: ' + nodeVersion);
  ^
Error: Unsupported Node version: 12.2.0
    at Object.<anonymous> (/home/travis/build/karma-runner/karma-mocha/node_modules/mock-fs/lib/index.js:38:9)

Current karma travis ci is configured for node 8 and 10 testing.

Solution

• Change CI to check only node 8 and 10
• Update mock-fs library to support node > 7

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[elpddev]

I signed it!

[karmarunnerbot]

🎉 This PR is included in version 2.0.0 🎉

The release is available on:

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

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