Fix content-encoding setter for regular headers

Author: AndrewBarba

lib/response.js

@@ -477,7 +477,7 @@ class RESPONSE {
         if (this._response.multiValueHeaders) {
           this._response.multiValueHeaders['content-encoding'] = [contentEncoding]
         } else {
-          this._response.headers['content-encoding'] = [contentEncoding]
+          this._response.headers['content-encoding'] = contentEncoding
         }
       }
     }