Use platforms instead of install_if (#8140)

Merge pull request 8140

lib/jekyll/commands/new.rb

@@ -91,13 +91,13 @@ module Jekyll
 
             # Windows and JRuby does not include zoneinfo files, so bundle the tzinfo-data gem
             # and associated library.
-            install_if -> { RUBY_PLATFORM =~ %r!mingw|mswin|java! } do
+            platforms :mingw, :x64_mingw, :mswin, :jruby do
               gem "tzinfo", "~> 1.2"
               gem "tzinfo-data"
             end
 
             # Performance-booster for watching directories on Windows
-            gem "wdm", "~> 0.1.1", :install_if => Gem.win_platform?
+            gem "wdm", "~> 0.1.1", :platforms => [:mingw, :x64_mingw, :mswin]
 
           RUBY
         end