Update split-api.gemspec

Author: andrew

split-api.gemspec

@@ -19,7 +19,7 @@ Gem::Specification.new do |gem|
   gem.add_dependency 'sinatra'
   gem.add_dependency 'multi_json'
 
-  gem.add_development_dependency 'bundler',     '~> 2.0'
+  gem.add_development_dependency 'bundler'
   gem.add_development_dependency 'rspec',       '~> 3.8.0'
   gem.add_development_dependency 'rack-test',   '~> 1.1'
   gem.add_development_dependency 'rake',        '~> 12.0'