Support older browsers

[marcioapm]

Upgrading from 1.20 to 1.30 breaks on older browsers (IE10), because it doesn't support Map and Set, even though it's never used in the app.

I think the checks instanceof Set and instanceof Map should be preceded by a typeof Map !== "undefined" to ensure it is a platform that supports these.

[mcollina]

Would you like to send a Pull Request to address this issue? Remember to add unit tests.