Update omniauth requirement from ~> 1.0 to >= 1, < 3

Updates the requirements on [omniauth](https://github.com/omniauth/omniauth) to permit the latest version.
- [Release notes](https://github.com/omniauth/omniauth/releases)
- [Commits](omniauth/omniauth@v1.0.0...v2.1.1)

---
updated-dependencies:
- dependency-name: omniauth
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

omniauth-uaa-oauth2.gemspec

@@ -15,7 +15,7 @@ Gem::Specification.new do |gem|
   gem.require_paths = ["lib"]
   gem.version       = OmniAuth::Cloudfoundry::VERSION
 
-  gem.add_runtime_dependency 'omniauth', '~> 1.0'
+  gem.add_runtime_dependency 'omniauth', '>= 1', '< 3'
   gem.add_runtime_dependency 'cf-uaa-lib', ['>= 3.2', '< 5.0']
 
   gem.add_development_dependency 'rspec', '~> 2.6.0'