Remove backports gem and test against current Ruby versions

* backports adds a significant overhead to the start time of
an application using the Namely gem.

* Removes old end-of-life Ruby versions from CI tests (1.9.3, 2.0.0)

* Adds new Ruby versions to test against (2.4.0, 2.3.3, 2.2.6, jruby9k)

Author: Oli Peate

.travis.yml

@@ -1,5 +1,6 @@
 rvm:
-  - 1.9.3
-  - jruby-19mode
-  - 2.0.0
-  - 2.1.3
+  - jruby-9.1.5.0
+  - 2.1.10
+  - 2.2.6
+  - 2.3.3
+  - 2.4.0

lib/namely.rb

@@ -1,4 +1,3 @@
-require "backports"
 require "json"
 require "ostruct"
 require "rest_client"

namely.gemspec

@@ -17,7 +17,6 @@ Gem::Specification.new do |spec|
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = ["lib"]
 
-  spec.add_dependency "backports"
   spec.add_dependency "rest-client"
 
   spec.add_development_dependency "bundler", "~> 1.7"