Fixed Session Cookie header

doc/api/README.md

@@ -101,7 +101,7 @@ Once you have your token, pass it to the API using either the `private_token`
 parameter or the `PRIVATE-TOKEN` header.
 
 
-### Session cookie
+### Session Cookie
 
 When signing in to GitLab as an ordinary user, a `_gitlab_session` cookie is
 set. The API will use this cookie for authentication if it is present, but using