/usr/lib/ruby/2.1.0/tkscrollbox.rb is in ruby2.1-tcltk 2.1.5-2+deb8u3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | #
# tkscrollbox.rb - load tk/scrollbox.rb
#
require 'tk/scrollbox'
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