Update permissions policy syntax in docs

[melissahenderson]

Permissions policy syntax is out of date on the following pages:

• https://webmonetization.org/docs/permission-policy
• https://webmonetization.org/docs/permission-policy-monetization

[melissahenderson]

I noticed a typo on the CSP: monetization-src page that I'm going to fix as well (an E in src)

Content-Security-Policy: monetization-srce <source>, <source>;