travis: use GO15VENDOREXPERIMENT

.travis.yml

@@ -17,8 +17,15 @@ addons:
     - libaspell-dev
     - libhunspell-dev
 
+env:
+ - GO15VENDOREXPERIMENT=1
+
 before_install:
  - go get -v github.com/chzchzchz/goword
 
+# disable godep restore override
+install:
+ - go get -t -v ./...
+
 script:
  - ./test