Fix template tag syntax

In 2.9 and earlier, Typescript allowed braces around the name introduced
by the `@template` tag, even though this syntax is non-standard. In 3.0,
Typescript introduces a more complex `@template` syntax that uses braces
for specifying the constraint of a type parameter:

```js
/** @template {Constraint} T -- By analogy with param syntax:
 *  @param {T} name
 */
function f(name) { ... }
```

That means that the syntax `/** @template {T} */` is illegal. This PR
fixes the uses of the `@template` tag ahead of Typescript 3.0 as well as
typescript@next.

lib/Chunk.js

@@ -69,7 +69,7 @@ const getModulesIdent = set => {
 };
 
 /**
- * @template {T}
+ * @template T
  * @param {Set<T>} set the set to convert to array
  * @returns {Array<T>} the array returned from Array.from(set)
  */

lib/ChunkGroup.js

@@ -18,7 +18,7 @@ const compareLocations = require("./compareLocations");
 let debugId = 5000;
 
 /**
- * @template {T}
+ * @template T
  * @param {Set<T>} set set to convert to array.
  * @returns {T[]} the array format of existing set
  */