import Config and test fix

[quentin-bettoum]

import Config instead of use Mix.Config as advised in the warning.

Updated required elixir version from 1.7 to 1.14

Change otp_release from 21.0 to 25.0

And apparently, the TypeError message changed in latest versions of node, thus making a test to fail, so I fixed it.

[quentin-bettoum]

I don't know where to update the node version for the travis build.

[grossvogel]

@quentin-bettoum thank you for your contributions!

these changes made it into v3.0.0 just not via this PR since we also had to fix the tooling before we could merge and deploy properly

• https://hex.pm/packages/nodejs/3.0.0
• https://github.com/revelrylabs/elixir-nodejs/releases/tag/v3.0.0b