ci: use latest go version

Go 1.14.2 was just released, fixing the panics we've
seen in module/apmrestful. Let's use the latest version
to keep with the times.

.jenkins.yml

@@ -6,3 +6,4 @@ GO_VERSION:
   - "1.10.x"
   - "1.11.x"
   - "1.12.x"
+  - "1.13.x"

Jenkinsfile

@@ -32,7 +32,7 @@ pipeline {
     issueCommentTrigger('(?i).*(?:jenkins\\W+)?run\\W+(?:the\\W+)?tests(?:\\W+please)?.*')
   }
   parameters {
-    string(name: 'GO_VERSION', defaultValue: "1.12.7", description: "Go version to use.")
+    string(name: 'GO_VERSION', defaultValue: "1.14.2", description: "Go version to use.")
     booleanParam(name: 'Run_As_Master_Branch', defaultValue: false, description: 'Allow to run any steps on a PR, some steps normally only run on master branch.')
     booleanParam(name: 'test_ci', defaultValue: true, description: 'Enable test')
     booleanParam(name: 'docker_test_ci', defaultValue: true, description: 'Enable run docker tests')

internal/tracecontexttest/Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.13
+FROM golang:latest
 ADD . /go/src/go.elastic.co/apm
 ENV GO111MODULE=on
 ENV GOPROXY=https://proxy.golang.org

scripts/Dockerfile-testing

@@ -1,5 +1,5 @@
 # Code generated by gendockerfile. DO NOT EDIT.
-FROM golang:1.13
+FROM golang:latest
 ENV GO111MODULE=on
 
 COPY go.mod go.sum /go/src/go.elastic.co/apm/

scripts/gendockerfile.go

@@ -59,7 +59,7 @@ var dockerfileTemplateFuncs = template.FuncMap{
 // copying across the rest of the source code.
 var dockerfileTemplate = template.Must(template.New("Dockerfile").Funcs(dockerfileTemplateFuncs).Parse(`
 # Code generated by gendockerfile. DO NOT EDIT.
-FROM golang:1.13
+FROM golang:latest
 ENV GO111MODULE=on
 {{range .Dirs}}
 COPY {{join . "go.mod"}} {{join . "go.sum"}} {{join "/go/src/go.elastic.co/apm" .}}/{{end}}