[dygraphs] Update legend option type (#20260)

* [dygraphs] update legend option

- add `never` to list of allowed string values for `legend` option
- ref: http://dygraphs.com/tests/legend-values.html

* [dygraphs] version update

- to publish new @types/dygraph package on npm

* [dygraphs] Updating comment for legend option

- adding comment for 'never' legend style.

* [dygraphs] correcting author url

types/dygraphs/index.d.ts

@@ -1,6 +1,6 @@
-// Type definitions for dygraphs 1.1.2
+// Type definitions for dygraphs 1.1.3
 // Project: http://dygraphs.com
-// Definitions by: Dan Vanderkam <http://danvk.org>
+// Definitions by: Dan Vanderkam <https://github.com/danvk>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 /// <reference types="google.visualization" />
@@ -595,9 +595,9 @@ declare namespace dygraphs {
         /**
          * When to display the legend. By default, it only appears when a user mouses over the chart.
          * Set it to "always" to always display a legend of some sort. When set to "follow", legend
-         * follows highlighted points.
+         * follows highlighted points. If set to 'never' then it will not appear at all.
          */
-        legend?: 'always' | 'follow' | 'onmouseover';
+        legend?: 'always' | 'follow' | 'onmouseover' | 'never';
 
         /**
          * for details see https://github.com/danvk/dygraphs/pull/683