LibWeb: Identify as "Ladybird" instead of "Browser"

Here's a small step towards integrating Ladybird and Browser. We now
identify ourselves as "Ladybird" to websites.

Userland/Libraries/LibWeb/Loader/ResourceLoader.h

@@ -44,7 +44,7 @@ namespace Web {
 #    error Unknown OS
 #endif
 
-constexpr auto default_user_agent = "Mozilla/5.0 (" OS_STRING "; " CPU_STRING ") LibWeb+LibJS/1.0 Browser/1.0";
+constexpr auto default_user_agent = "Mozilla/5.0 (" OS_STRING "; " CPU_STRING ") LibWeb+LibJS/1.0 Ladybird/1.0";
 
 class ResourceLoaderConnectorRequest : public RefCounted<ResourceLoaderConnectorRequest> {
 public: