bug fix - adding qr-canvas id

The dependency on element IDs goes deeper than I thought. I'm adding the qr-canvas ID back. It's not best practice, but I don't have time to restructure the code *that* much, and my previous change breaks the core functionality. I've tested this and it resolves all known issues.
Merge pull request #12 from cyborgx37/master

bug fix - adding qr-canvas id