README.md: Update compatibility matrix

Author: brancz

README.md

@@ -47,13 +47,14 @@ Currently, `client-go` is in version `release-5.0`.
 #### Compatibility matrix
 At most 5 kube-state-metrics releases will be recorded below.
 
-| kube-state-metrics | client-go | **Kubernetes 1.4**  | **Kubernetes 1.5** | **Kubernetes 1.6** | **Kubernetes 1.7** | **Kubernetes 1.8** |
-|--------------------|-----------|---------------------|--------------------|--------------------|--------------------|--------------------|
-| **v0.4.0** |  v2.0.0-alpha.1   |          ✓          |         ✓          |        -           |         -          |         -          |
-| **v0.5.0** |  v2.0.0-alpha.1   |          ✓          |         ✓          |        -           |         -          |         -          |
-| **v1.0.x** |  4.0.0-beta.0     |          ✓          |         ✓          |        ✓           |         ✓          |         -          |
-| **v1.1.0** |  release-5.0      |          ✓          |         ✓          |        ✓           |         ✓          |         ✓          |
-| **master** |  v5.0.0      |          ✓          |         ✓          |        ✓           |         ✓          |         ✓          |
+| kube-state-metrics | client-go | **Kubernetes 1.4**  | **Kubernetes 1.5** | **Kubernetes 1.6** | **Kubernetes 1.7** | **Kubernetes 1.8** | **Kubernetes 1.9** |
+|--------------------|-----------|---------------------|--------------------|--------------------|--------------------|--------------------|--------------------|
+| **v0.4.0** |  v2.0.0-alpha.1   |          ✓          |         ✓          |        -           |         -          |         -          |         -          |
+| **v0.5.0** |  v2.0.0-alpha.1   |          ✓          |         ✓          |        -           |         -          |         -          |         -          |
+| **v1.0.x** |  4.0.0-beta.0     |          ✓          |         ✓          |        ✓           |         ✓          |         -          |         -          |
+| **v1.1.0** |  release-5.0      |          ✓          |         ✓          |        ✓           |         ✓          |         ✓          |         -          |
+| **v1.2.0** |  v6.0.0           |          ✓          |         ✓          |        ✓           |         ✓          |         ✓          |         ✓          |
+| **master** |  v6.0.0           |          ✓          |         ✓          |        ✓           |         ✓          |         ✓          |         ✓          |
 - `✓` Fully supported version range.
 - `-` The Kubernetes cluster has features the client-go library can't use (additional API objects, etc).