[Openid-specs-fapi] Issue #558: update filenames for grant management and CIBA (openid/fapi)

[dgtonge]

New issue 558: update filenames for grant management and CIBA
https://bitbucket.org/openid/fapi/issues/558/update-filenames-for-grant-management-and

Dave Tonge:

in a similar manner as we had to do for the main FAPI 2 specs - [https://bitbucket.org/openid/fapi/pull-requests/390](https://bitbucket.org/openid/fapi/pull-requests/390)

Responsible: Dave Tonge