Update favicon to use the diffy logo

The new favicon was generated on https://www.favicon-generator.org
using the diffy_logo.png as source.

Change-Id: Ibea6b1948bb63e0d792c2700d537341842feb225
diff --git a/images/favicon.ico b/images/favicon.ico
index 0d505be..f2a09cf 100644
--- a/images/favicon.ico
+++ b/images/favicon.ico
Binary files differ