Remove dependency to fastlane

With an upcoming _fastlane_ release it is important to remove the dependency to _fastlane_ and _fastlane_core_, see fastlane/fastlane#7412 for more information

badge.gemspec

@@ -20,7 +20,6 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^bin/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
-  spec.add_dependency 'fastlane_core', '>= 0.44.0', '< 1.0.0' # all shared code and dependencies
   spec.add_dependency 'fastimage', '~> 1.6' # fetch the image sizes
   spec.add_dependency 'mini_magick', '~> 4.5' # to add badge image on app icon