Add rollForward note in README, improve proxy health check in e2e tests and bump version to v5.3.0 (#738)

* docs: add note about latest* rollForward support in global.json

* update health check options for squid proxy in e2e tests

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "setup-dotnet",
-  "version": "5.0.1",
+  "version": "5.3.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "setup-dotnet",
-      "version": "5.0.1",
+      "version": "5.3.0",
       "license": "MIT",
       "dependencies": {
         "@actions/cache": "^5.0.5",