The NPM WebJar is easier to deploy. As soon as the CodeMirror author
publishes a new version to NPM, anyone can deploy it to WebJars in one
click. In contrast, the classic WebJar requires a WebJars team member to
manually update and deploy it, which usually takes longer [1].
Also update version to 5.13.4, which was a trivial fix to include the
LICENSE file and brought no functionality change.
[1]: http://www.webjars.org/
Change-Id: I9328f371aa99cac7e81b3f8a442d6582275ad3a7
fae6bb2365