Update rake-compiler to 1.0.3

This obsoletes setting ruby version constraints, because it's
done by rake-compiler itself.

Gemfile

@@ -13,7 +13,7 @@ gem "hoe-gemspec", "~>1.0.0", :group => [:development, :test]
 gem "hoe-git", "~>1.6.0", :group => [:development, :test]
 gem "minitest", "~>5.8.4", :group => [:development, :test]
 gem "rake", "~>10.5.0", :group => [:development, :test]
-gem "rake-compiler", "~>0.9.2", :group => [:development, :test]
+gem "rake-compiler", "~>1.0.3", :group => [:development, :test]
 gem "rake-compiler-dock", "~>0.6.0", :group => [:development, :test]
 gem "racc", "~>1.4.14", :group => [:development, :test], :platform => [:ruby, :mingw, :x64_mingw]
 gem "rexical", "~>1.0.5", :group => [:development, :test], :platform => [:ruby, :mingw, :x64_mingw]

Rakefile

@@ -164,7 +164,7 @@ HOE = Hoe.spec 'nokogiri' do
     ["hoe-git",            "~> 1.6.0"],
     ["minitest",           "~> 5.8.4"],
     ["rake",               "~> 10.5.0"],
-    ["rake-compiler",      "~> 0.9.2"],
+    ["rake-compiler",      "~> 1.0.3"],
     ["rake-compiler-dock", "~> 0.6.0"],
     ["racc",               "~> 1.4.14"],
     ["rexical",            "~> 1.0.5"]
@@ -258,11 +258,6 @@ else
       ext.cross_compiling do |spec|
         libs = dependencies.map { |name, dep| "#{name}-#{dep["version"]}" }.join(', ')
 
-        spec.required_ruby_version = [
-          '>= 2.1.0',
-          "< #{CROSS_RUBIES.max_by(&:ver).minor_ver.succ}"
-        ]
-
         spec.post_install_message = <<-EOS
 Nokogiri is built with the packaged libraries: #{libs}.
         EOS