'preserveHostHdr' is not exposed in the user options

[9chu]

The option preserveHostHdr is not assigned in the function resolveOptions but used in the function reqHeaders to determine if the proxy should bypass the Host param in the HTTP request header.

Which makes me cannot proxy requests from different domains to the same backend service.

The following patch will fix the issue:

--- lib/resolveOptions.js   2021-04-23 15:26:31.249257700 +0800
+++ lib/resolveOptions.js   2021-04-23 15:26:33.412777400 +0800        
@@ -15,6 +15,7 @@
   options = options || {};

   return {
+    preserveHostHdr: options.preserveHostHdr,
     proxyReqPathResolver:  options.proxyReqPathResolver,
     proxyReqOptDecorator: options.proxyReqOptDecorator,
     proxyReqBodyDecorator: options.proxyReqBodyDecorator,