Updates screen shot with more a more realistic call graph

See https://github.com/openzipkin/zipkin/pull/1026
diff --git a/public/img/web-screenshot.png b/public/img/web-screenshot.png
index fb292e3..7a34242 100644
--- a/public/img/web-screenshot.png
+++ b/public/img/web-screenshot.png
Binary files differ