Remove dep and use go modules in .travis.yml

.travis.yml

@@ -1,22 +1,25 @@
+os: linux
+dist: xenial
 language: go
 
 go:
 - 1.9.x
+- 1.13.x
+
+go_import_path: "github.com/pterodactyl/wings"
 
 services:
-  - docker
+- docker
 
 install:
 - mkdir -p $GOPATH/bin
 
 # Install used tools
-- go get github.com/golang/dep/cmd/dep
 - go get github.com/mitchellh/gox
 - go get github.com/haya14busa/goverage
 - go get github.com/schrej/godacov
 
-# Install project dependencies with dep
-- dep ensure
+- go mod download
 
 script:
 - make cross-build