Clean up some invalid ascii character sequences.

Rubocop was reporting a fatal error:
  lib/util/win32/wim_parser.rb:1:1: F: "\xe2" on us-ascii.

To diagnose, I read the each byte of the file, reporting any outside ascii range.

r = File.read("lib/util/win32/wim_parser.rb")
r.each_byte {|b| if b > 126; print "!!! #{b}"; else print b.chr; end;}; nil

The relevant characters and their surrounding context:
  "Value is set to !!! 226�!!! 156MSWIM\0\0!!! 226�!!! 157"

  "This flag is primarily used in the Windows!!! 194!!! 160Deployment Services (WDS) scenario"