Use tools section for Jenkins

Jenkinsfile

@@ -17,12 +17,12 @@ limitations under the License.
 pipeline {
     agent any
 
-    def root = tool type: 'go', name: 'Go 1.16'
+    tools {
+        go "Go 1.16"
+    }
 
     environment {
-        GOROOT= "${root}"
+        GO11MODULE = "on"
-        GOPATH = "${pwd(tmp: true)}/gocode"
-        PATH = "${root}/bin:${PATH}"
     }
 
     stages {