doc/roadmap: put "App Engine support" under "Done".

R=rsc, dsymonds
CC=golang-dev
https://golang.org/cl/4528053

doc/devel/roadmap.html

@@ -43,8 +43,6 @@ Improved garbage collector.
 <li>
 Debugger.
 <li>
-App Engine support.
-<li>
 Improved implementation documentation.
 </ul>
 
@@ -132,4 +130,6 @@ A means of recovering from a panic (recover).
 Improved CGO including some mechanism for calling back from C to Go.
 <li>
 Faster, allocation-light reflection.
+<li>
+App Engine support.
 </ul>