app/views/devise/mailer/unlock_instructions.html.erb
<% require 'devise/version' %>
<p><%= t('.greeting', :recipient => @resource.email, :default => "Hello #{@resource.email}!") %></p>
<p><%= t('.message', :default => "Your account has been locked due to an excessive amount of unsuccessful sign in attempts.") %></p>
<p><%= t('.instruction', :default => "Click the link below to unlock your account:") %></p>
<p><%= link_to t('.action', :default => "Unlock my account"), unlock_url(@resource, :unlock_token => (Devise::VERSION.start_with?('3.') ? @token :@resource.unlock_token)) %></p>