minor fix to accept but ignore time in since date of historical service API
minor fix to accept but ignore time in since date of historical service API

SmartInfrastructures/FIWARELab-monitoringAPI,SmartInfrastructures/FIWARELab-monitoringAPI,attybro/xifi-monitoringAPI,attybro/FIWARELab-monitoringAPI,SmartInfrastructures/FIWARELab-monitoringAPI