Convert invalid strings from binary to utf-8

Since changing the encoding from UTF8 to UTF8 doesn't do anything (see
http://bugs.ruby-lang.org/issues/7967#note-1), change the source encoding
to binary (ie. ascii-8bit) and replace all undefined characters.

lib/cane/encoding_aware_iterator.rb

@@ -15,7 +15,7 @@ def each(&block)
         begin
           line =~ /\s/
         rescue ArgumentError
-          line.encode!('UTF-8', 'UTF-8', invalid: :replace)
+          line.encode!('UTF-8', 'binary', invalid: :replace, undef: :replace)
         end
 
         block.call(line)