Test and update to a current Node.js version #71

The Openframe install script currently installs Node.js 6. Node.js 6 has reached EOL in April 2019 and is no longer receiving maintenance updates. We should update. Current Node.js versions are 12 and 13.

1. First, someone would have to test if there are any issues with the latest Node.js versions. In case that fails, we could at least try to update to some other version higher than 6.
2. As a second step, the script the install script can be updated. Should be easy.