[chart.js] Added Line Chart Options (#18704)

* Added Line Chart Options

http://www.chartjs.org/docs/latest/charts/line.html#configuration-options
showLines - Boolean - If false, the lines between points are not drawn.
spanGaps - Boolean - If false, NaN data causes a break in the line.

* Moved location of property

* Update definitions by

types/chart.js/index.d.ts

@@ -3,6 +3,7 @@
 // Definitions by: Alberto Nuti <https://github.com/anuti>
 //                 Fabien Lavocat <https://github.com/FabienLavocat>
 //                 KentarouTakeda <https://github.com/KentarouTakeda/>
+//                 Larry Bahr <https://github.com/larrybahr/>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.3
 
@@ -158,6 +159,8 @@ declare namespace Chart {
         animation?: ChartAnimationOptions;
         elements?: ChartElementsOptions;
         scales?: ChartScales;
+        showLines?: boolean;
+        spanGaps?: boolean;
         cutoutPercentage?: number;
         circumference?: number;
         rotation?: number;