update Lfg_Solo.cpp

Thanks to Artanisx for updates https://github.com/Artanisx/mod-solo-lfg/blob/master/src/Lfg_Solo.cpp
Extra Credits added

src/Lfg_Solo.cpp

@@ -3,6 +3,7 @@
 ** AzerothCore 2019 http://www.azerothcore.org/
 ** Conan513 https://github.com/conan513
 ** Made into a module by Micrah https://github.com/milestorme/
+** Updated to work with AzerothCore Docker Installations by Artanisx https://github.com/Artanisx/
 */
 
 #include "ScriptMgr.h"
@@ -18,7 +19,9 @@ class lfg_solo : public PlayerScript
 public:
     lfg_solo() : PlayerScript("lfg_solo") { }
 
-   void OnLogin(Player* player)
+   // Docker Installation prevents warnings. In order to avoid the issue, we need to add __attribute__ ((unused)) 
+   // to the player variable to tell the compiler it is fine not to use it.
+   void OnLogin(Player* __attribute__ ((unused))player)
    {
 	   if (sConfigMgr->GetIntDefault("LFG.SoloMode", true))
         {