Link heatmap from master instead of dev

Author: markus-wa

README.md

@@ -82,7 +82,7 @@ Running the above code (`go run heatmap.go > heatmap.png`) will create a PNG wit
 
 This doesn't look too interesting on it's own but that can be helped by quickly mapping it to the map overview in an image editing tool (2 min tops, no skills required).
 
-![Resulting heatmap before and after mapping to map overview](https://raw.githubusercontent.com/markus-wa/demoinfocs-golang/dev/examples/heatmap/heatmap.jpg)
+![Resulting heatmap before and after mapping to map overview](https://raw.githubusercontent.com/markus-wa/demoinfocs-golang/master/examples/heatmap/heatmap.jpg)
 
 ## Features