Apply no-buffer-constructor lint rule

lib/soap.js

@@ -524,7 +524,7 @@ function response(rpc) {
     SOAPServer: SERVER_NAME
   };
 
-  if (!rpc) return { code: 204, headers: headers, data: new Buffer(0) };
+  if (!rpc) return { code: 204, headers: headers, data: Buffer.allocUnsafe(0) };
 
   const env = createSoapEnv(rpc.cwmpVersion);
   const header = env.node("soap-env:Header");
@@ -589,7 +589,7 @@ function response(rpc) {
   return {
     code: 200,
     headers: headers,
-    data: new Buffer(env.doc().toString(LIBXMLJS_SAVE_OPTIONS))
+    data: env.doc().toString(LIBXMLJS_SAVE_OPTIONS)
   };
 }