app/helpers/application_helper.rb
module ApplicationHelper
def gravatar_for(user, options = { size: 80 })
gravatar_id = Digest::MD5.hexdigest(user.email.downcase)
size = options[:size]
gravatar_url = "https://secure.gravatar.com/avatar/#{gravatar_id}?s=#{size}"
image_tag(gravatar_url, alt: user.name, class: 'img-circle')
end
end