Added glide for vendoring dependencies.

- Docker to 1.13.x

glide.yaml

@@ -0,0 +1,28 @@
+package: github.com/stffabi/watchtower
+import:
+- package: github.com/Sirupsen/logrus
+  version: ~0.11.x
+- package: github.com/docker/docker
+  version: ~1.13.x
+  subpackages:
+  - api/types
+  - api/types/container
+  - api/types/network
+  - api/types/reference
+  - cli/command
+  - cliconfig
+  - cliconfig/configfile
+  - cliconfig/credentials
+  - client
+- package: github.com/stretchr/testify
+  version: ~1.1.4
+  subpackages:
+  - mock
+- package: github.com/urfave/cli
+  version: ~1.19.1
+- package: golang.org/x/net
+  repo: https://github.com/tonistiigi/net.git
+  subpackages:
+  - context
+- package: github.com/robfig/cron
+  version: 9585fd555638e77bba25f25db5c44b41f264aeb7