Don't rebuild vendor in Travis

Since we check vendor in, there's no need to rebuild the vendor
directory.

.travis.yml

@@ -6,19 +6,8 @@ go:
 # blech, Travis downloads with capitals in DirectXMan12, which confuses go
 go_import_path: github.com/directxman12/k8s-prometheus-adapter
 
-before_install:
-- curl -L -s https://github.com/golang/dep/releases/download/v0.4.1/dep-linux-amd64 -o $GOPATH/bin/dep
-- chmod +x $GOPATH/bin/dep
-
-install:
-- make -B vendor
-
 script: make verify
 
-cache:
-  directories:
-  - ~/gopath/pkg/dep/
-
 sudo: required
 services:
 - docker