fix a spelling error (GoogleCloudPlatform#197)

Author: lesv

appengine/multitenancy/src/main/webapp/WEB-INF/web.xml

@@ -44,6 +44,6 @@
  <filter-name>NamespaceFilter</filter-name>
  <url-pattern>/sign</url-pattern>
  </filter-mapping>
-<!-- [END filter] -->
+<!-- [END nsfilter] -->
 
 </web-app>