Update ATT&CK™ to ATT&CK®

[isaisabel]

As a user of the ATT&CK website, I want to see accurate legal language relfecting the status of the ATT&CK trademark.

All instances of ATT&CK™ should be updated with ATT&CK®. See Butterick's Practical Typography for best practices on placement.

[isaisabel]

This also applies to page titles:

$ curl -s https://attack.mitre.org/groups/G0018/ | grep \<title\>
<title>admin@338 | MITRE ATT&CK&trade;</title>