feature/yarn-workspaces

[rbnts]

• switch out lerna in favor of yarn workspaces
• remove unnecessary dependencies
• remove unnecessary config files
• clean up metadata and file structure

[lbsonley]

check travis build logs for graphicmagick related error. Add it back to travis.yml if needed

[lbsonley]

I think we still need to install graphicsmagick for the image optimization task.

[lbsonley]

we should consider adding multiple node versions here. Travis will do a build for each version listed. I think we should keep all LTS versions of node here. This way we can say we support LTS.

[rbnts]

agreed, let's go for 12.x and 14.x

[lbsonley]

@robinloeffel , I forgot to bump the engines prop in package.json everywhere when I did the node upgrade. Since we are updating the travis config for node version, I think we should bump the engines field for all packages.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

Robin Löffel seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}