upgrade go version to 1.13 in external-dns

.travis.yml

@@ -6,7 +6,7 @@ os:
 language: go
 
 go:
-- "1.12.x"
+- "1.13.x"
 - tip
 
 matrix:
@@ -14,11 +14,11 @@ matrix:
   - go: tip
 
 env:
-- GO111MODULE=on GOLANGCI_RELEASE="v1.17.1"
+- GOLANGCI_RELEASE="v1.17.1"
 
 before_install:
-- go get github.com/mattn/goveralls
-- go get github.com/lawrencewoodman/roveralls
+- GO111MODULE=off go get github.com/mattn/goveralls
+- GO111MODULE=off go get github.com/lawrencewoodman/roveralls
 - curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | sh -s -- -b $(go env GOPATH)/bin ${GOLANGCI_RELEASE}
 
 script:

Dockerfile

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 # builder image
-FROM golang:1.12.9 as builder
+FROM golang:1.13 as builder
 
 WORKDIR /github.com/kubernetes-incubator/external-dns
 

Dockerfile.mini

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM golang:1.12.9 as builder
+FROM golang:1.13 as builder
 
 WORKDIR /github.com/kubernetes-incubator/external-dns
 

README.md

@@ -162,7 +162,6 @@ support](https://github.com/golang/go/wiki/Modules#installing-and-activating-mod
 Assuming Go has been setup with module support it can be built simply by running:
 
 ```console
-$ export GO111MODULE=on # needed if the project is checked out in your $GOPATH.
 $ make
 ```
 

go.mod

@@ -1,6 +1,6 @@
 module github.com/kubernetes-incubator/external-dns
 
-go 1.12
+go 1.13
 
 require (
 	cloud.google.com/go v0.37.4