remove default value

include/vstd/DateUtils.h

@@ -5,7 +5,7 @@ VCMI_LIB_NAMESPACE_BEGIN
 namespace vstd
 {
 
-	DLL_LINKAGE std::string getFormattedDateTime(std::time_t dt, std::string format = "");
+	DLL_LINKAGE std::string getFormattedDateTime(std::time_t dt, std::string format);
 	DLL_LINKAGE std::string getDateTimeISO8601Basic(std::time_t dt);
 
 }