Add libicu-dev to the .gitlab-ci.yml

.gitlab-ci.yml

@@ -6,6 +6,7 @@
     ELASTIC_CONNECTION_INFO: '{"url":["http://elasticsearch:9200"]}'
   stage: test
   script:
+    - apt-get update && apt-get -yy install libicu-dev
     - make setup
     - make format
     - make test