Change OnStatusCommand to use non-const variable like most of the EModRet modulecalls

git-svn-id: https://znc.svn.sourceforge.net/svnroot/znc/trunk@1262 726aef4b-f618-498e-8847-2d620e286838

modules/shell.cpp

@@ -114,7 +114,7 @@ public:
 		}
 	}
 
-	virtual EModRet OnStatusCommand(const CString& sCommand) {
+	virtual EModRet OnStatusCommand(CString& sCommand) {
 		if (sCommand.Equals("SHELL")) {
 			PutShell("-- ZNC Shell Service --");
 			return HALT;