tests: use Go 1.9.6

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

.travis.yml

@@ -6,7 +6,7 @@ sudo: required
 services: docker
 
 go:
-- 1.9.5
+- 1.9.6
 
 notifications:
   on_success: never

tests/semaphore.test.bash

@@ -15,7 +15,7 @@ fi
 docker run \
   --rm \
   --volume=`pwd`:/go/src/github.com/coreos/etcd \
-  gcr.io/etcd-development/etcd-test:go1.9.5 \
+  gcr.io/etcd-development/etcd-test:go1.9.6 \
   /bin/bash -c "${TEST_OPTS} ./test 2>&1 | tee test-${TEST_SUFFIX}.log"
 
 ! egrep "(--- FAIL:|panic: test timed out|appears to have leaked)" -B50 -A10 test-${TEST_SUFFIX}.log