Incoherent urls in main html when using more than 1 blueprint, with different blueprint url_prefix

[lounagen]

Hi, When you define more than 1 blueprint without the same api_prefix (for REST API versioning) and different api_spec_url (when testing a tunned api_spec_url and forgetting old /api/spec on in the other blueprint), the last blueprint registration override the api_spec_static global variable and in the .js urls of the main html, you get incoherent api_spec_url according to the non-last blueprints api_prefix

proposal with this comit: https://github.com/lounagen/flask-restful-swagger/commit/11d41ef9f6c2b82390ebcf62bd238b1c687eadb5

(inside pull request https://github.com/rantav/flask-restful-swagger/pull/62 )

regards