[doc] Fix broken link (#1897)

Author: Mesteery

README.md

@@ -23,7 +23,7 @@ can use one of the many wrappers available on npm, like
 
 - [Protocol support](#protocol-support)
 - [Installing](#installing)
-  - [Opt-in for performance and spec compliance](#opt-in-for-performance-and-spec-compliance)
+  - [Opt-in for performance](#opt-in-for-performance)
 - [API docs](#api-docs)
 - [WebSocket compression](#websocket-compression)
 - [Usage examples](#usage-examples)