Use wget instead of curl to wait for container

Because even Ubuntu 20.04 version of `curl` is outdated

.travis.yml

@@ -10,7 +10,7 @@ before_install:
   - docker-compose ps
 
 script:
-  - curl --retry 3 --retry-all-errors http://localhost:8002
+  - wget --timeout 3 --tries=5 --spider localhost:8002 2>&1 | grep -i http
   - docker-compose logs --no-color
   - docker logs chtsh
   - CHEATSH_TEST_STANDALONE=NO bash tests/run-tests.sh