Re-enable flasgger

[scolby33]

Disabled for now because it pulls in an old version of pyYAML that has a security vulnerability.

https://nvd.nist.gov/vuln/detail/CVE-2017-18342

It can be re-enabled when either pyYAML has released a non-beta fixed version or when flasgger switches to yaml.safe_load everywhere instead of yaml.load.

[cthoyt]

Is flasgger still under development, or is it stale?

[scolby33]

Last commit in November 2018. In any case, it's less their fault than pyYAML's anyway. Maybe I'll open a pull over at flasgger.