FYI: rerun install.sh after pulling latest github changes

[Chris Smith]

Hey everyone!  If you don't run your own copy of the CodeWorld server, you can ignore this.

If you pull the latest changes to github to a locally installed CodeWorld server, you'll need to rerun part of install.sh to avoid losing editor features.  There's a new section at the end to install CodeMirror.

The issue is that CodeMirror used to operate its own minifier that let you choose modes and add-ons, and get a minified result.  But that's been discontinued, so to update it to a new version, I had to incorporate generating a new CodeMirror compressed file into the install process.

I just filed https://github.com/google/codeworld/issues/435 to track making this process less painful in the future.