add browserstack (#1121)

README.md

@@ -104,6 +104,8 @@ npm test
 
 ## Browsers support
 
+This project is tested with BrowserStack.
+
 | [<img src="https://raw.githubusercontent.com/alrra/browser-logos/master/src/firefox/firefox_48x48.png" alt="Firefox" width="24px" height="24px" />](http://godban.github.io/browsers-support-badges/)<br/>Firefox | [<img src="https://raw.githubusercontent.com/alrra/browser-logos/master/src/chrome/chrome_48x48.png" alt="Chrome" width="24px" height="24px" />](http://godban.github.io/browsers-support-badges/)<br/>Chrome | [<img src="https://raw.githubusercontent.com/alrra/browser-logos/master/src/safari/safari_48x48.png" alt="Safari" width="24px" height="24px" />](http://godban.github.io/browsers-support-badges/)<br/>Safari |
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 | last 4 versions                                                                                                                                                                                                   | last 4 versions                                                                                                                                                                                               | 12.1+                                                                                                                                                                                                         |