Update README.md

Author: evanw

README.md

@@ -1,5 +1,5 @@
 # Source Map Visualization
 
-Demo: [https://evanw.github.io/source-map-visualization/](http://evanw.github.io/source-map-visualization/)
+Demo: [https://evanw.github.io/source-map-visualization/](https://evanw.github.io/source-map-visualization/)
 
 This is a visualization of JavaScript/CSS source map data, which is useful for debugging problems with generated source maps. It's designed to be high-performance so it doesn't fall over with huge source maps.