Small fix needed to enable GHES

[pberthonneau]

Hi

I have been generating the lib and doc with the Open API description for GHES 3.3.
All is fine except a small thing impacting pure GHES enterprise capabilities:

build_lib.py generates the metadata.py with for example

 ('/users/{username}/suspended', 'put', 'enterprise-admin/suspend-user', 'Suspend a user', '[email protected]/rest/reference/enterprise-admin#suspend-a-user', [], [['reason', str]], ''),

which is converted in doc as

• enterprise-admin.suspend_user(username, reason): Suspend a user

The problem is with the minus in enterprise-admin. In Python a method cannot have a minus in its name.
When I replace with enterprise_admin everything is fine and I can call the API.

Then I think a specific replacement of - by _ should be added to https://github.com/fastai/ghapi/blob/master/90_build_lib.ipynb