Suppress warnings on old version of Ruby

fzf

@@ -830,7 +830,7 @@ class FZF
             when ''
               nil
             when /^\^(.*)\$$/
-              Regexp.new('^' << sanitize(Regexp.escape $1) << '$', rxflag)
+              Regexp.new('^' << sanitize(Regexp.escape($1)) << '$', rxflag)
             when /^'/
               w.length > 1 ?
                 Regexp.new(sanitize(Regexp.escape(w[1..-1])), rxflag) : nil

fzf.gemspec

 # coding: utf-8
 Gem::Specification.new do |spec|
   spec.name          = 'fzf'
-  spec.version       = '0.5.2'
+  spec.version       = '0.5.3'
   spec.authors       = ['Junegunn Choi']
   spec.email         = ['junegunn.c@gmail.com']
   spec.description   = %q{Fuzzy finder for your shell}