build: revert all attempts to disable docs travis-ci will remain broken for nightly (3.12) testing. Trying to enable maintainer mode broke on a missing dot executable. Disable nightly since something is borked in the base config there and I don't want to waste credits on it.

try:
    # Python 3+
    from ssl import SSLError
except (ImportError, AttributeError):
    # Python 2.5-2.7
    from socket import sslerror as SSLError    # noqa: F401