[CI] Updated Elasticsearch on Travis to 5.5.3

Author: Dawn Richardson

.travis.yml

@@ -30,14 +30,14 @@ matrix:
 
     - rvm: 2.4.0
       jdk: oraclejdk8
-      env: TEST_SUITE=integration SERVER=start TEST_CLUSTER_LOGS=/tmp/log TEST_BUILD_REF=origin/5.x TEST_CLUSTER_COMMAND=/tmp/elasticsearch-5.4.0-SNAPSHOT/bin/elasticsearch
+      env: TEST_SUITE=integration SERVER=start TEST_CLUSTER_LOGS=/tmp/log TEST_BUILD_REF=origin/5.5 TEST_CLUSTER_COMMAND=/tmp/elasticsearch-5.5.3/bin/elasticsearch
 
 before_install:
   - gem update --system
   - gem --version
   - gem install bundler -v 1.14.3
   - bundle version
-  - curl -sS https://snapshots.elastic.co/downloads/elasticsearch/elasticsearch-5.4.0-SNAPSHOT.tar.gz | tar xz -C /tmp
+  - curl -sS https://artifacts.elastic.co/downloads/elasticsearch/elasticsearch-5.5.3.tar.gz | tar xz -C /tmp
   - rake setup
   - rake elasticsearch:update