ScanQR: Modification of regex throwing warning

[phutelmyer]

Describe the change
Update url regular expression in ScanQR to fix warning observed during tests:

=============================== warnings summary ===============================
/strelka/strelka/scanners/scan_qr.py:19: DeprecationWarning: invalid escape sequence '\/'
  URL_REGEX = '^((https?|ftp|smtp):\/\/)?(www.)?[a-z0-9]+\.[a-z]+(\/[a-zA-Z0-9#]+\/?)*'

The updated regular expression will match the same addresses as before, it's just removing extraneous escape characters.

Describe testing procedures
Submitted several QR documents to Strelka.

Sample output
N/A

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of and tested my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings