Edited readme with 3 updated browser icons. (#4414)

In the main readme file of axios, the icons for chrome, firefox and safari was not visible, which was giving a bit outdated vibes. I have updated all the three icons with the latest ones from  "https://www.iconfinder.com/icons/23799/firefox_icon" in 48px dimension. I hope now it looks good.

Co-authored-by: Jay <jasonsaayman@gmail.com>

README.md

@@ -65,7 +65,7 @@ Promise based HTTP client for the browser and node.js
 
 ## Browser Support
 
-![Chrome](https://raw.github.com/alrra/browser-logos/master/src/chrome/chrome_48x48.png) | ![Firefox](https://raw.github.com/alrra/browser-logos/master/src/firefox/firefox_48x48.png) | ![Safari](https://raw.github.com/alrra/browser-logos/master/src/safari/safari_48x48.png) | ![Opera](https://raw.github.com/alrra/browser-logos/master/src/opera/opera_48x48.png) | ![Edge](https://raw.github.com/alrra/browser-logos/master/src/edge/edge_48x48.png) | ![IE](https://raw.github.com/alrra/browser-logos/master/src/archive/internet-explorer_9-11/internet-explorer_9-11_48x48.png) |
+![Chrome](https://cdn2.iconfinder.com/data/icons/social-icons-33/128/Google_Chrome-48.png) | ![Firefox](https://cdn2.iconfinder.com/data/icons/humano2/48x48/apps/firefox-icon.png) | ![Safari](https://cdn3.iconfinder.com/data/icons/3d-applications/48/app_icons_web_development___safari_logo_browser_application_app_apple.png) | ![Opera](https://raw.github.com/alrra/browser-logos/master/src/opera/opera_48x48.png) | ![Edge](https://raw.github.com/alrra/browser-logos/master/src/edge/edge_48x48.png) | ![IE](https://raw.github.com/alrra/browser-logos/master/src/archive/internet-explorer_9-11/internet-explorer_9-11_48x48.png) |
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