update changelog for 3.5.0 release

CHANGELOG.md

@@ -8,6 +8,36 @@ The format is based on [these versioning and changelog guidelines](https://git.i
 
 ---
 
+## 3.5.0 - 2019-01-16
+
+### Enhancements
+
+- Update build toolchain to use Babel v7, PostCSS v7 and Rollup v1. Update our build targets match our [supported browsers](https://help.shopify.com/en/manual/intro-to-shopify/shopify-admin/supported-browsers), leading to a reduction in bundle size ([#837](https://github.com/Shopify/polaris-react/pull/837))
+
+### Bug fixes
+
+- Ensure disabled `Button` components with a `url` prop output valid HTML ([#773](https://github.com/Shopify/polaris-react/pull/773))
+- Fixed `DropZone` which was unable to add a duplicate file back to back or add a file again once removed [#782](https://github.com/Shopify/polaris-react/pull/782). Thank you [@jzsplk](https://github.com/jzsplk) for the contribution [#425](https://github.com/Shopify/polaris-react/issues/425) and [@vladucu](https://github.com/vladucu) for the clear example.
+- Added a fallback to the `safeAreaFor` sass mixin to handle browsers that don't support `env` and `constant` [#881](https://github.com/Shopify/polaris-react/pull/881)
+
+### Documentation
+
+- Added deprecation guidelines ([#853](https://github.com/Shopify/polaris-react/pull/853))
+
+### Development workflow
+
+- Replaced our home-grown playground with Storybook (still accessed through `yarn dev`) ([#768](https://github.com/Shopify/polaris-react/pull/768))
+- Removed our usage of babel-node for build scripts - use plain node instead ([#836](https://github.com/Shopify/polaris-react/pull/836))
+- Ensure CSS builds are reproducible ([#869](https://github.com/Shopify/polaris-react/pull/869))
+
+### Code quality
+
+- Upgraded the `Banner`, `Card`, and `Modal` components from legacy context API to use createContext ([#786](https://github.com/Shopify/polaris-react/pull/786))
+
+### Deprecations
+
+- Deprecated `Navigation.UserMenu` in favor of `TopBar.UserMenu` ([#849](https://github.com/Shopify/polaris-react/pull/849))
+
 ## 3.4.0 - 2019-01-08
 
 ### Enhancements