Remove backports dependency

* Nothing within the library depends on it anymore, so remove this
  for now. Things may change if 1.9 or 2.0 specific methods are
  used in the future.

adamantium.gemspec

@@ -16,8 +16,7 @@ Gem::Specification.new do |gem|
   gem.test_files       = `git ls-files -- spec/{unit,integration}`.split($/)
   gem.extra_rdoc_files = %w[LICENSE README.md TODO]
 
-  gem.add_runtime_dependency('backports', [ '~> 3.0', '>= 3.0.3' ])
-  gem.add_runtime_dependency('ice_nine',  '~> 0.7.0')
+  gem.add_runtime_dependency('ice_nine', '~> 0.7.0')
 
   gem.add_development_dependency('rake',  '~> 10.0.3')
   gem.add_development_dependency('rspec', '~> 1.3.2')