Use another way to get latest docker on Travis

.travis.yml

@@ -4,10 +4,11 @@ language: minimal
 services:
   - docker
 
-addons:
-  apt:
-    packages:
-      - docker-ce
+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
 
 script:
   - make docker-build