fix region endpoint initialization in contentstack.js

Author: harshithad0703

lib/contentstack.js

@@ -164,7 +164,8 @@ export function client (params = {}) {
   let defaultHostName = getRegionEndpoint('na')
 
   if (params.region) {
-    defaultHostName = getRegionEndpoint(params.region.toLowerCase())
+    params.region = params.region.toLowerCase()
+    defaultHostName = getRegionEndpoint(params.region)
   }
 
   const defaultParameter = {