fix HTTPSend copy

WiFiManager.cpp

@@ -1291,7 +1291,7 @@ String WiFiManager::getHTTPHead(String title){
   return page;
 }
 
-void WiFiManager::HTTPSend(String content){
+void WiFiManager::HTTPSend(const String &content){
   server->send(200, FPSTR(HTTP_HEAD_CT), content);
 }
 

WiFiManager.h

@@ -646,7 +646,7 @@ class WiFiManager
     void          updateConxResult(uint8_t status);
 
     // webserver handlers
-    void          HTTPSend(String content);
+    void          HTTPSend(const String &content);
     void          handleRoot();
     void          handleWifi(boolean scan);
     void          handleWifiSave();