Use godep to vendor in dependencies

We also bump travis to test with go 1.6 and tip as it allows us to build
without explicitly setting the vendoring experiment env var.

Author: Tonkpils

.travis.yml

@@ -3,13 +3,10 @@ language: go
 sudo: false
 
 go:
-  - 1.5
+  - 1.6
   - tip
 
 install: true
 
-before_install:
-  - go get -t ./...
-
 script:
-  - go test ./...
+  - go test $(go list ./... | grep -v /vendor/)

Godeps/Godeps.json

@@ -14,7 +14,7 @@ Python or Ruby environment simply to fetch and submit exercises.
 
 ## Dependencies
 
-Go version 1.5 or higher
+Go version 1.6 or higher
 
 ## Installing Go