DOCS: remove thin from copyright

DOCS: remove thin from copyright

it is no longer used

diff --git a/COPYRIGHT.txt b/COPYRIGHT.txt
index b22e221..cb867e5 100644
--- a/COPYRIGHT.txt
+++ b/COPYRIGHT.txt
@@ -29,5 +29,3 @@ Javascript
 Ruby
 
   Rails - Copyright (c) 2005-2013 David Heinemeier Hansson, Rails Core Team contributors (MIT)
-
-  Thin - Copyright (c) 2012-2013 Marc-Andre Cournoyer

GitHub sha: 97f045d0