Missing Line Terminator on allowedOrigins enables origin spoofing

@pkkr identified a vulnerability in our Snaps `allowedOrigins` functionality, a functionality which allows a Snap developers to control which origins could interact with certain Snaps APIs. Due to a missing regex terminator, this origin control could be bypassed, allowing a malicious domain to access restricted parts of the Snaps API. At its worst, this would enable malicious dApps to call the Keyring API’s `exportAccount` method, potentially accessing sensitive account information from Snaps who choose to implement it. Not only did @pkkr identify this impactful vulnerability, but did so with incredible timing. His prompt report allowed us to address the issue before it reached production. We would like to thank @pkkr for his continued efforts to demonstrate the impact of this vulnerability and for consistently helping to make MetaMask more secure.