LibWeb: Add "image/x‑portable‑bitmap" mime type for pbm file extension

Author: https://github.com/asliturk
Commit: https://github.com/SerenityOS/serenity/commit/41d55316241
Pull-request: https://github.com/SerenityOS/serenity/pull/2606

Libraries/LibWeb/Loader/Resource.cpp

@@ -79,6 +79,8 @@ String mime_type_from_content_type(const String& content_type)
 
 static String guess_mime_type_based_on_filename(const URL& url)
 {
+    if (url.path().ends_with(".pbm"))
+        return "image/x‑portable‑bitmap";
     if (url.path().ends_with(".png"))
         return "image/png";
     if (url.path().ends_with(".gif"))