install latest docker manually

.travis.yml

@@ -1,6 +1,11 @@
 sudo: required
-services:
-  - docker
+before_install:
+  - curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
+  - sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
+  - sudo apt-get update
+  - sudo apt-get -y -o Dpkg::Options::="--force-confnew" install docker-ce
+#services:
+#  - docker
 language: java
 jdk:
   - openjdk8