ci(typescript): add typescript_next build

Install typescript@next before build.js and test.typings.
Restore the regular version before travis caches node_modules/.

Fixes #6368

modules/playground/src/web_workers/images/services/bitmap.ts

@@ -63,7 +63,7 @@ export class BitmapService {
     return imageData;
   }
 
-  private _swap(data: any[], index1: number, index2: number) {
+  private _swap(data: Uint8Array | number[], index1: number, index2: number) {
     var temp = data[index1];
     data[index1] = data[index2];
     data[index2] = temp;