Fix #195 - explicitly state /a/{var} does not match /a/b/

Looking at the Tomcat unit tests I see there is an explicit test that
/a/{var} does not match /a/b/ as a result of EG discussion.

Signed-off-by: Mark Thomas <markt@apache.org>

spec/src/main/asciidoc/WebSocket.adoc

@@ -510,6 +510,7 @@ matches this is /a/b/
 with reserved characters "/" are not valid URI-template level 1
 expansions):
 ** /a
+** /a/b/
 ** /a/b/c