use HTTPS for Petstore by default (#4652)

docs/usage/cors.md

@@ -21,7 +21,7 @@ You can verify CORS support with one of three techniques:
 - Curl your API and inspect the headers.  For instance:
 
 ```bash
-$ curl -I "http://petstore.swagger.io/v2/swagger.json"
+$ curl -I "https://petstore.swagger.io/v2/swagger.json"
 HTTP/1.1 200 OK
 Date: Sat, 31 Jan 2015 23:05:44 GMT
 Access-Control-Allow-Origin: *

docs/usage/installation.md

@@ -44,7 +44,7 @@ you could do something like this:
 var SwaggerUIBundle = require('swagger-ui-dist').SwaggerUIBundle
 
 const ui = SwaggerUIBundle({
-    url: "http://petstore.swagger.io/v2/swagger.json",
+    url: "https://petstore.swagger.io/v2/swagger.json",
     dom_id: '#swagger-ui',
     presets: [
       SwaggerUIBundle.presets.apis,