Update defs for new hookKeepAlive config option (#4794)

All tests pass on re-run. :-)

Author: TylerBrock

src/Options/Definitions.js

@@ -302,6 +302,11 @@ module.exports.ParseServerOptions = {
     "env": "PARSE_SERVER_LIVE_QUERY_SERVER_OPTIONS",
     "help": "Live query server configuration options (will start the liveQuery server)",
     "action": parsers.objectParser
+  },
+  "hookKeepAlive": {
+    "env": "PARSE_SERVER_HOOK_KEEP_ALIVE",
+    "help": "Keep hook HTTP connections alive",
+    "action": parsers.booleanParser
   }
 };
 module.exports.CustomPagesOptions = {