Update docs to reflect current ES compatibility and runtimes

docs/release-source/release.md

@@ -25,28 +25,24 @@ This page contains the entire Sinon.JS API documentation along with brief introd
 
 {% include docs/migration-guides.md %}
 
-### Compatibility
+## Compatibility
 
-### ES5.1
+The most up-to-date reference on which runtimes and browsers we support can be found by looking at our shared [eslint-config][shared-config].
 
-Sinon `{{page.release_id}}` is written as [ES5.1][es5] and requires no transpiler or polyfills to run in the runtimes listed below.
+### ECMAScript versions
 
-### Supported runtimes
+Sinon has historically been written as [ES5][es5], but starting from Sinon 10 we made the breaking change to use more modern ECMAScript versions, starting with ECMAScript [2017][es2017]. `{{page.release_id}}` requires no transpiler or polyfills to run in the runtimes mentioned below.
 
-`{{page.release_id}}` has been verified in these runtimes:
+### Supported runtimes
 
-- Firefox 45
-- Chrome 48
-- Internet Explorer 11
-- Edge 14
-- Safari 9
-- [Node.js LTS versions](https://github.com/nodejs/Release)
+As of Sinon 10 we stopped maintaining compatibility with legacy browsers. Instead, we focus on compatibility with evergreen browsers, [Node.js LTS versions](https://github.com/nodejs/Release) and recent Safari versions.
 
 There should not be any issues with using Sinon `{{page.release_id}}` in newer versions of the same runtimes.
 
-If you need to support very old runtimes that have incomplete support for [ES5.1][es5] you might get away with using loading [`es5-shim`][es5-shim] in your test environment.
+If you need to support old runtimes you can try one of the older Sinon versions.
 
 {% include docs/contribute.md %}
 
 [es5]: http://www.ecma-international.org/ecma-262/5.1/
-[es5-shim]: https://github.com/es-shims/es5-shim
+[es2017]: http://www.ecma-international.org/ecma-262/8.0/
+[shared-config]: https://github.com/sinonjs/eslint-config