Tests fail when run under Node v6.10.2 or earlier

[aduth]

Regression introduced in #399 (a71bea2)

Steps to reproduce:

1. Install Node v6.10.2 (easiest with n or nvm)
2. Run npm run test-unit

Expected result:

Tests pass, especially considering we define a preferred version via .nvmrc.

Actual result:

Tests fail with error:

TypeError: Object.values is not a function

Anticipated cause:

Support for the Object.values function was not added until Node 7.x .

See also: http://node.green/#ES2017-features-Object-static-methods-Object-values

Removing the transform-runtime Babel plugin from the test build means that this method is not polyfilled. We'll need to consider how to reconcile this with the Babel issue described here:

babel/babel#2877 (comment)

[aduth]

Related to this, our Travis configuration should probably be such that it aligns with the version defined in .nvmrc if this is the version we want to assign as "preferred".

[nylen]

After nvm install 7 (which put me on version 7.9.0), I had to run npm rebuild node-sass to make the build/tests work.

[youknowriad]

Closing as fixed