Fix warnings from gem build

opentracing.gemspec

@@ -10,7 +10,7 @@ Gem::Specification.new do |spec|
 
   spec.summary       = 'OpenTracing Ruby Platform API'
   spec.homepage      = 'https://github.com/opentracing/opentracing-ruby'
-  spec.license       = 'Apache 2.0'
+  spec.license       = 'Apache-2.0'
 
   spec.files         = `git ls-files -z`.split("\x0").reject do |f|
     f.match(%r{^(test|spec|features)/})
@@ -19,10 +19,10 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ['lib']
 
-  spec.add_development_dependency 'bundler'
+  spec.add_development_dependency 'bundler', '~> 0'
   spec.add_development_dependency 'minitest', '~> 5.0'
   spec.add_development_dependency 'rake', '~> 10.0'
   spec.add_development_dependency 'rubocop', '~> 0.54.0'
-  spec.add_development_dependency 'simplecov'
-  spec.add_development_dependency 'simplecov-console'
+  spec.add_development_dependency 'simplecov', '~> 0'
+  spec.add_development_dependency 'simplecov-console', '~> 0'
 end