update supported calico version to 3.7.3 in README (#4966)

README.md

@@ -115,7 +115,7 @@ Supported Components
     -   [cri-o](http://cri-o.io/) v1.11.5 (experimental: see [CRI-O Note](docs/cri-o.md). Only on centos based OS)
 -   Network Plugin
     -   [cni-plugins](https://github.com/containernetworking/plugins) v0.8.1
-    -   [calico](https://github.com/projectcalico/calico) v3.4.0
+    -   [calico](https://github.com/projectcalico/calico) v3.7.3
     -   [canal](https://github.com/projectcalico/canal) (given calico/flannel versions)
     -   [cilium](https://github.com/cilium/cilium) v1.3.0
     -   [contiv](https://github.com/contiv/install) v1.2.1