update video_info version to 2.6

List of 2.6 features can be found here thibaudgg/video_info#103

Author: 0mega

link_thumbnailer.gemspec

@@ -22,6 +22,6 @@ Gem::Specification.new do |spec|
   spec.add_dependency 'rake',                   '>= 0.9'
   spec.add_dependency 'nokogiri',               '~> 1.6'
   spec.add_dependency 'net-http-persistent',    '~> 2.9'
-  spec.add_dependency 'video_info',             '~> 2.4'
+  spec.add_dependency 'video_info',             '~> 2.6'
   spec.add_dependency 'image_info',             '~> 1.0'
 end