Properly set Go version in CI.

.ci/Jenkinsfile

@@ -30,14 +30,18 @@ pipeline {
         gitCheckout(basedir: "${BASE_DIR}", githubNotifyFirstTimeContributor: true)
         pipelineManager([ cancelPreviousRunningBuilds: [ when: 'PR' ] ])
         stash allowEmpty: true, name: 'source', useDefaultExcludes: false
+        dir("${BASE_DIR}"){
+          setEnvVar('GO_VERSION', readFile(".go-version").trim())
+        }
       }
     }
     stage('Lint'){
       steps {
         withGithubNotify(context: "Lint") {
           dir("${BASE_DIR}"){
-            withMageEnv(){
-              sh(label: 'Check', script: 'mage -v check')
+            withMageEnv(version: "${env.GO_VERSION}"){
+              cmd(label: 'mage notice', script: 'mage notice')
+              cmd(label: 'mage check', script: 'mage -v check')
             }
           }
         }
@@ -51,7 +55,7 @@ pipeline {
     //      deleteDir()
     //      unstash 'source'
     //      dir("${BASE_DIR}"){
-    //        withMageEnv(){
+    //        withMageEnv(version: "${env.GO_VERSION}"){
     //          sh(label: 'Build', script: 'mage -v check')
     //        }
     //    }