fix java 8 compatibility

Author: ahorek

Gemfile

@@ -12,7 +12,7 @@ end
 
 group :development, :test do
   gem "coveralls", require: false
-  gem "rake-compiler", require: false
+  gem "rake-compiler", "~> 1.1.9", require: false
   gem "rspec", "~> 3.7", require: false
   gem "rubocop", "0.82.0", require: false
 end

rakelib/extension.rake

@@ -4,8 +4,7 @@ if defined? JRUBY_VERSION
   require "rake/javaextensiontask"
   Rake::JavaExtensionTask.new("nio4r_ext") do |ext|
     ext.ext_dir = "ext/nio4r"
-    ext.source_version = "1.8"
-    ext.target_version = "1.8"
+    ext.release = '8'
   end
 else
   require "rake/extensiontask"