deps: update coredns to version 1.6.2

Our current deployed version for coredns is `1.3.1`
which seems to be very old.

Since we plan a minor release, we should bump the version of Coredns
to a recent release.

Note: since this branch runs K8S 1.16, we bind the coredns version
to `1.6.2` following same standards from kubeadm.

Closes: #2572

buildchain/buildchain/versions.py

@@ -99,8 +99,8 @@ def _version_prefix(version: str, prefix: str = 'v') -> str:
     ),
     Image(
         name='coredns',
-        version='1.3.1',
-        digest='sha256:02382353821b12c21b062c59184e227e001079bb13ebd01f9d3270ba0fcbf1e4',
+        version='1.6.2',
+        digest='sha256:12eb885b8685b1b13a04ecf5c23bc809c2e57917252fd7b0be9e9c00644e8ee5',
     ),
     Image(
         name='dex',