Update README.md

Fix FEX button URL.

Author: adamdanz

README.md

@@ -1,6 +1,6 @@
 # Thermometer Chart
 
-[![View Thermometer Chart on File Exchange](https://www.mathworks.com/matlabcentral/images/matlab-file-exchange.svg)]
+[![View Thermometer Chart on File Exchange](https://www.mathworks.com/matlabcentral/images/matlab-file-exchange.svg)](https://www.mathworks.com/matlabcentral/fileexchange/101889-thermometer-chart)
 [![Open in MATLAB OnlinE](https://www.mathworks.com/images/responsive/global/open-in-matlab-online.svg)](https://matlab.mathworks.com/open/github/v1?repo=MATLAB-Graphics-and-App-Building/thermometer-chart&file=Examples.mlx) 
 
 Version: 1.0