Use stricter noreferrer flag for external links

Author: djmattyg007

mopidy_api_explorer/static/index.html

@@ -45,7 +45,7 @@ <h1>WebSocket endpoint</h1>
                     You can use this endpoint to access Mopidy's full API, and
                     to get notified about events happening in Mopidy.
                     <br>
-                    <a href="https://docs.mopidy.com/en/latest/api/http/#websocket-api" target="_blank" rel="noopener">More info</a>
+                    <a href="https://docs.mopidy.com/en/latest/api/http/#websocket-api" target="_blank" rel="noreferrer">More info</a>
                 </p>
             </div>
 
@@ -58,7 +58,7 @@ <h1>HTTP POST RPC endpoint</h1>
                     While you can't listen to events via this endpoint, it
                     doesn't require maintaining a persistent connection.
                     <br>
-                    <a href="https://docs.mopidy.com/en/latest/api/http/#http-post-api" target="_blank" rel="noopener">More info</a>
+                    <a href="https://docs.mopidy.com/en/latest/api/http/#http-post-api" target="_blank" rel="noreferrer">More info</a>
                 </p>
             </div>
 
@@ -76,7 +76,7 @@ <h1>JavaScript API</h1>
                     <pre>window.mopidy = new Mopidy();</pre>
                 </div>
                 <p>
-                    More info can be found at the <a href="https://docs.mopidy.com/en/latest/api/js/" target="_blank" rel="noopener">Mopidy.js documentation</a>
+                    More info can be found at the <a href="https://docs.mopidy.com/en/latest/api/js/" target="_blank" rel="noreferrer">Mopidy.js documentation</a>
                 </p>
             </div>
 
@@ -101,7 +101,7 @@ <h2>Documentation</h2>
 
                 <p>
                     For more information, please refer to the Mopidy documentation at
-                    <a href="https://docs.mopidy.com/" target="_blank" rel="noopener">docs.mopidy.com</a>.
+                    <a href="https://docs.mopidy.com/" target="_blank" rel="noreferrer">docs.mopidy.com</a>.
                 </p>
             </div>
         </main>