Update README.md

README.md

@@ -21,7 +21,7 @@
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 <h2>Preview</h2>
-<p align="center"><img src="https://raw.githubusercontent.com/ayushsharma82/WebSerial/master/docs/webserial.png?sanitize=true" width="450"></p>
+<p align="center"><img src="https://raw.githubusercontent.com/ayushsharma82/WebSerial/master/docs/webserial.PNG?sanitize=true" width="850"></p>
 
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