add ruby 2.5 to package build on mac

Rakefile

@@ -113,7 +113,7 @@ task 'gem:native' do
   if RUBY_PLATFORM =~ /darwin/
     FileUtils.touch 'grpc_c.32.ruby'
     FileUtils.touch 'grpc_c.64.ruby'
-    system "rake cross native gem RUBY_CC_VERSION=2.4.0:2.3.0:2.2.2:2.1.5:2.0.0 V=#{verbose} GRPC_CONFIG=#{grpc_config}"
+    system "rake cross native gem RUBY_CC_VERSION=2.5.0:2.4.0:2.3.0:2.2.2:2.1.6:2.0.0 V=#{verbose} GRPC_CONFIG=#{grpc_config}"
   else
     Rake::Task['dlls'].execute
     docker_for_windows "gem update --system && bundle && rake cross native gem RUBY_CC_VERSION=2.4.0:2.3.0:2.2.2:2.1.5:2.0.0 V=#{verbose} GRPC_CONFIG=#{grpc_config}"

tools/distrib/build_ruby_environment_macos.sh

@@ -47,7 +47,7 @@ EOF
 
 MAKE="make -j8"
 
-for v in 2.4.0 2.3.0 2.2.2 2.1.5 2.0.0-p645 ; do
+for v in 2.5.0 2.4.0 2.3.0 2.2.2 2.1.6 2.0.0-p645 ; do
   ccache -c
   rake -f $CROSS_RUBY cross-ruby VERSION=$v HOST=x86_64-darwin11
 done