authorization: Fix endpoint path

The path for the endpoint shown in the example is slightly confusing
as it is a traditional REST endpoint. Usually MCP servers are free
to define _one_ MCP endpoint. Commonly `/`, `/sse`, `/messages` or `/mcp`
are used. In this ase we choose `/mcp` to stay away from any indication
if we are using SSE or not.

Author: dsp-ant

docs/specification/draft/basic/authorization.mdx

@@ -214,7 +214,7 @@ even if they are part of the same logical session.
 Example request:
 
 ```http
-GET /v1/contexts HTTP/1.1
+GET /mcp HTTP/1.1
 Host: mcp.example.com
 Authorization: Bearer eyJhbGciOiJIUzI1NiIs...
 ```