Minor fixes

Minor fixes.

1. This is a `@Deprecated` method and very meaningless to modify, but I changed internal cast of `Collection.multiply(Number)` from `List` to `Collection`. This was a bug.
2. Removed meaningless `@SupressWarning` of `Collection.grep()`.
3. `<<` to `&lt;&lt;` in JavaDoc.
4. Fixed some wrong JavaDoc.