Fix typo

Related to #266. Looks like I've changed the prefix afterward at some point for some reason, but engine is retarded and with `plugin.something.cfg` it will understand extension is `something` instead  of `cfg` ; and will fail to execute as it's an invalid extension (only `cfg` and `rc` are allowed).

amxmodx/amxmodx.cpp

@@ -4506,7 +4506,7 @@ static cell AMX_NATIVE_CALL AutoExecConfig(AMX *amx, cell *params)
 		}
 
 		static char newName[PLATFORM_MAX_PATH];
-		UTIL_Format(newName, sizeof(newName), "plugin.%s", pluginName);
+		UTIL_Format(newName, sizeof(newName), "plugin-%s", pluginName);
 
 		name = newName;
 	}