Revert "Update omniauth dependency to fix CVE-2015-9284"

This reverts commit 2dcd499.

The CVE hasn't actually been fixed yet..

omniauth/omniauth#809

Author: patch0

omniauth-rpi.gemspec

@@ -30,7 +30,7 @@ Gem::Specification.new do |spec|
   spec.require_paths = ['lib']
 
   spec.add_dependency 'jwt'
-  spec.add_dependency 'omniauth', '~> 1.9'
+  spec.add_dependency 'omniauth', '~> 1.4'
   spec.add_dependency 'omniauth-oauth2', '~> 1.4'
 
   spec.add_development_dependency 'bundler', '~> 2.0'