Use go mod (#265)

appveyor.yml

@@ -8,6 +8,7 @@ environment:
   GOPATH: c:\gopath
   DEPTESTBYPASS501: 1
   GOVERSION: 1.12
+  GO111MODULE: on
 
 init:
   - git config --global core.autocrlf input
@@ -27,9 +28,6 @@ build: false
 deploy: false
 
 test_script:
-  - go get github.com/davecgh/go-spew/spew
-  - go get gopkg.in/yaml.v2
-  - go get github.com/BurntSushi/toml
   - go test github.com/pelletier/go-toml
   - go test github.com/pelletier/go-toml/cmd/tomljson
   - go test github.com/pelletier/go-toml/cmd/tomll