As part of upgrading to kubectl 1.13
in https://gitlab.com/gitlab-org/gitlab/issues/30495
we also should raise the minimum cluster version, as
https://kubernetes.io/docs/setup/release/version-skew-policy/#kubectl
means we support 1.12, 1.13 and 1.14

See also https://gitlab.com/gitlab-org/charts/gitlab/issues/1389