Set GO15VENDOREXPERIMENT=1 earlier in travis script.

.travis.yml

@@ -5,6 +5,7 @@ go:
 sudo: false
 before_install:
   - gotools=golang.org/x/tools
+  - export GO15VENDOREXPERIMENT=1
 install:
   - go get -v github.com/Masterminds/glide
   - glide install
@@ -14,5 +15,4 @@ install:
   - go get -v github.com/davecgh/go-spew/spew
 script:
   - export PATH=$PATH:$HOME/gopath/bin
-  - export GO15VENDOREXPERIMENT=1
   - ./goclean.sh