Disable builds for classic App Engine.

Current build file doesn't build the subdirectories, therefore succeeds
without building the actual packages. We need to add the appengine
and appengine_internal manually to the GOPATH and enable the
appengine build again.
diff --git a/.travis.yml b/.travis.yml
index 3d835cb..9ab73b2 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,7 +2,7 @@
 go: 1.3
 
 install:
-  go get -v -tags='appengine appenginevm' ./... && hg clone https://code.google.com/p/appengine-go/ $GOPATH/appengine
+  - go get -v -tags='appengine appenginevm' ./...
 
 script:
-  go test -v -tags='appengine appenginevm' ./... && go build -v -tags='appengine'
+  - go test -v -tags='appengine appenginevm' ./...