Update gem spec to handle java

.ruby-version

@@ -1 +1 @@
-2.2.3
+2.3.1

.travis.yml

@@ -4,4 +4,5 @@ rvm:
   - 2.1.0
   - 2.2.4
   - 2.3.1
+  - jruby-9.1.3.0
 before_install: gem install bundler -v 1.10.6

tdigest.gemspec

@@ -3,13 +3,15 @@ lib = File.expand_path('../lib', __FILE__)
 $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 require 'tdigest/version'
 
+java = (ENV['RUBY_PLATFORM'] == 'java')
+
 Gem::Specification.new do |spec|
   spec.name          = "tdigest"
   spec.version       = TDigest::VERSION
   spec.authors       = ["Sebastian Wallin"]
   spec.email         = ["sebastian.wallin@gmail.com"]
 
-  spec.summary       = %q{Ruby implementation of Dunning's T-Digest for streaming quantile approximation}
+  spec.summary       = %q{TDigest for Ruby}
   spec.description   = %q{Ruby implementation of Dunning's T-Digest for streaming quantile approximation}
   spec.homepage      = "https://github.com/castle/tdigest"
   spec.license       = "MIT"
@@ -18,12 +20,20 @@ Gem::Specification.new do |spec|
   spec.bindir        = "exe"
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
+  spec.platform      = java ? 'java' : 'ruby'
+
+
+  if java
+    spec.add_runtime_dependency 'rbtree-jruby', '~> 0.2.1'
+  else
+    spec.add_runtime_dependency 'rbtree', '~> 0.4.2'
+  end
 
   spec.add_runtime_dependency 'rbtree', '~> 0.4.2'
 
   spec.add_development_dependency 'bundler', '~> 1.10'
   spec.add_development_dependency 'rake', '~> 10.0'
-  spec.add_development_dependency 'minitest', '~> 5.8.3'
+  spec.add_development_dependency 'minitest', '~> 5.8'
   spec.add_development_dependency 'coveralls', '~> 0.8.10'
   spec.add_development_dependency 'simplecov', '~> 0.11.1'
 end