travis.yml: remove "./cmd"

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

.travis.yml

@@ -51,7 +51,7 @@ before_install:
 - docker pull gcr.io/etcd-development/etcd-test:go1.9.3
 
 install:
-- pushd cmd/etcd && go get -t -v ./... && popd
+- go get -t -v ./...
 
 script:
  - >