[changed] package.browser to package.unpkg
browser refers to which APIs a library uses. The module build already uses browser-safe APIs, except for import statements. Any tool that cares about the browser field will be able to resolve import statements.
CDNs like unpkg will serve the JS file directly. This change ensures they still have a bundled version to serve, without potentially duplicating dependencies when we're bundled downstream.
Tags: Material Motion
Differential Revision: http://codereview.cc/D3508