minor changes on line_chart_data.dart
minor changes on line_chart_data.dart

imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart