kubekins/krte: Build go1.15.13 variants

Author: thejoycekung

images/kubekins-e2e/variants.yaml

@@ -34,13 +34,13 @@ variants:
     OLD_BAZEL_VERSION: 2.2.0
   '1.20':
     CONFIG: '1.20'
-    GO_VERSION: 1.15.12
+    GO_VERSION: 1.15.13
     K8S_RELEASE: stable-1.20
     BAZEL_VERSION: 3.4.1
     OLD_BAZEL_VERSION: 2.2.0
   '1.19':
     CONFIG: '1.19'
-    GO_VERSION: 1.15.12
+    GO_VERSION: 1.15.13
     K8S_RELEASE: stable-1.19
     BAZEL_VERSION: 2.2.0
     OLD_BAZEL_VERSION: 0.23.2