Update README.md

README.md

 
 Need help ? Do not hesitate to contact me : damien.accorsi@free.fr
 
-![BrowserStack](https://github.com/tracim/tracim/tree/master/tracim/tracim/public/assets/img/logo_browserstack.svg)
+<a href='https://www.browserstack.com' target="_blank">
+    <img src="https://raw.githubusercontent.com/tracim/tracim/master/tracim/tracim/public/assets/img/logo_browserstack.png" width="150">
+</a>
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 BrowserStack support open source project and graciously helps us testing Tracim on every devices.