Ruby: update Gemspec.

ruby/google-protobuf.gemspec

 Gem::Specification.new do |s|
   s.name        = "google-protobuf"
   s.version     = "3.2.0"
-  s.licenses    = ["BSD"]
+  s.licenses    = ["BSD-3-Clause"]
   s.summary     = "Protocol Buffers"
   s.description = "Protocol Buffers are Google's data interchange format."
   s.homepage    = "https://developers.google.com/protocol-buffers"
@@ -15,12 +15,12 @@ Gem::Specification.new do |s|
   else
     s.files     += Dir.glob('ext/**/*')
     s.extensions= ["ext/google/protobuf_c/extconf.rb"]
-    s.add_development_dependency "rake-compiler-dock", "~> 0.5.1"
+    s.add_development_dependency "rake-compiler-dock", "~> 0.6.0"
   end
   s.test_files  = ["tests/basic.rb",
                   "tests/stress.rb",
                   "tests/generated_code_test.rb"]
   s.add_development_dependency "rake-compiler", "~> 0.9.5"
-  s.add_development_dependency "test-unit", "~> 3.0.9"
+  s.add_development_dependency "test-unit", '~> 3.0', '>= 3.0.9'
   s.add_development_dependency "rubygems-tasks", "~> 0.2.4"
 end