Update Docker version in Travis

Author: arthurbarr

.travis.yml

@@ -8,6 +8,10 @@ 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 install docker-ce
   - curl https://glide.sh/get | sh
   - curl -LO https://github.com/golang/dep/releases/download/v0.3.0/dep-linux-amd64.zip
   - unzip dep-linux-amd64.zip