hack(travis): temporarily fix travis

try a quick workaround for https://github.com/travis-ci/travis-ci/issues/1727

.travis.yml

@@ -6,3 +6,8 @@ install:
 
 script:
  - ./test.sh
+
+# temporarily fix Travis
+env:
+  global:
+      - TRAVIS_BUILD_DIR=/home/travis/build/coreos/etcd