Fix build, use -mod=readonly (grafana#98)

* use -mod=readonly

* Create .go-version

* Update go.mod

* Update .go-version

Author: tonglil

.go-version

@@ -0,0 +1 @@
+1.14.2

.travis.yml

@@ -4,10 +4,10 @@ services:
 - docker
 language: go
 go:
-  - "1.11.x"
+  - "1.14.x"
 
 env:
-  - GOFLAGS=-mod=vendor
+  - GOFLAGS=-mod=readonly
 
 install:
 # This script is used by the Travis build to install a cookie for
@@ -24,6 +24,7 @@ script:
 branches:
   only:
   - master
+
 matrix:
   fast_finish: true
   allow_failures:

go.mod

@@ -1,5 +1,7 @@
 module github.com/terraform-providers/terraform-provider-grafana
 
+go 1.14
+
 require (
 	github.com/hashicorp/hcl v1.0.0 // indirect
 	github.com/hashicorp/terraform v0.12.2