Read first: https://github.com/gorhill/uBlock/blob/master/CONTRIBUTING.md

Describe the issue

If I try to sign the extension with jpm sign it fails with an error.
I see the embeded webextensions for example are not signed and I guess they are not since the uBlock Origin devs sign the addon in AMO. If we fix this issue you can provide signed extensions just like this one.

Steps for anyone to reproduce the issue

1. Install NodeJS and run npm i -g jpm.
2. Grab you credentials from AMO
3. jpm sign --api-key $AMO_API_KEY --api-secret $AMO_API_SECRET --xpi uBlock0.webext.xpi
   Obviously replace $AMO_API_KEY and $AMO_API_SECRET from step 2.
4. Boom! Error!
   bash JPM [error] FAIL Error: Could not find root RDF element in install.rdf at /usr/lib/node_modules/jpm/lib/utils.js:202:15 at tryCatchReject (/usr/lib/node_modules/jpm/node_modules/when/lib/makePromise.js:845:30) at runContinuation1 (/usr/lib/node_modules/jpm/node_modules/when/lib/makePromise.js:804:4) at Fulfilled.when (/usr/lib/node_modules/jpm/node_modules/when/lib/makePromise.js:592:4) at ContinuationTask.run (/usr/lib/node_modules/jpm/node_modules/when/lib/makePromise.js:702:24) at Scheduler._drain (/usr/lib/node_modules/jpm/node_modules/when/lib/Scheduler.js:62:19) at Scheduler.drain (/usr/lib/node_modules/jpm/node_modules/when/lib/Scheduler.js:27:9) at doNTCallback0 (node.js:417:9) at process._tickCallback (node.js:346:13)
   I'll send a pull request for this soon because I know the fix also :D