Missing dollar sign

.travis.yml

@@ -19,7 +19,7 @@ env:
 
 before_script:
   - mkdir ${HOME}/elasticsearch
-  - wget https://download.elastic.co/elasticsearch/elasticsearch/elasticsearch-{ES_VERSION}.tar.gz
+  - wget https://download.elastic.co/elasticsearch/elasticsearch/elasticsearch-${ES_VERSION}.tar.gz
   - tar -xzf elasticsearch-${ES_VERSION}.tar.gz -C ${HOME}/elasticsearch
   - ${HOME}/elasticsearch/elasticsearch-${ES_VERSION}/bin/elasticsearch >/dev/null &