fix OpenAPI JSON file rendering (#775)

pygeoapi/api.py

@@ -690,7 +690,7 @@ class API:
         if isinstance(openapi, dict):
             return headers, 200, to_json(openapi, self.pretty_print)
         else:
-            return headers, 200, openapi.read()
+            return headers, 200, openapi
 
     @pre_process
     def conformance(self,

pygeoapi/flask_app.py

@@ -134,8 +134,8 @@ def openapi():
     with open(os.environ.get('PYGEOAPI_OPENAPI'), encoding='utf8') as ff:
         if os.environ.get('PYGEOAPI_OPENAPI').endswith(('.yaml', '.yml')):
             openapi_ = yaml_load(ff)
-        else:  # JSON file, do not transform
-            openapi_ = ff
+        else:  # JSON string, do not transform
+            openapi_ = ff.read()
 
     return get_response(api_.openapi(request, openapi_))