Add readBodyBuffer method to HttpClientResponse (#1475)

* Add readBodyBuffer method to HttpClientResponse

* Implement method in other package tests

* Make method optional to satisfy the test process

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@actions/http-client",
-  "version": "2.1.0",
+  "version": "2.1.1",
   "description": "Actions Http Client",
   "keywords": [
     "github",