Updated frameworks.yaml to include more appropriate branch for phpbb

The phpbb devs mentioned that develop branch is potentially unstable with new features and that develop-ascraeus is more stable as it is the development branch for the next stable version, 3.1 (ascraeus).
https://wiki.phpbb.com/PhpBB3.1    

It also includes the fixes @joelm submitted to them as mentioned in frameworks.yaml.
```
# Stable is release-3.0.12, but we have pull requests in develop
# https://github.com/phpbb/phpbb/pull/1908
# https://github.com/phpbb/phpbb/pull/2232
```