Don't leak a global variable

Author: etiennebarrie

lib/coderay/scanners/ruby.rb

@@ -257,7 +257,7 @@ def scan_tokens encoder, options
               end
               unless unicode
                 # check for unicode
-                $DEBUG_BEFORE, $DEBUG = $DEBUG, false
+                debug_before, $DEBUG = $DEBUG, false
                 begin
                   if check(/./mu).size > 1
                     # seems like we should try again with unicode
@@ -266,7 +266,7 @@ def scan_tokens encoder, options
                 rescue
                   # bad unicode char; use getch
                 ensure
-                  $DEBUG = $DEBUG_BEFORE
+                  $DEBUG = debug_before
                 end
                 next if unicode
               end