Add link text to change password mail template

Included a default fallback to provide a base English translation for
users that are using a locale file that does not define this new key.

app/views/clearance_mailer/change_password.html.erb

@@ -1,5 +1,8 @@
-<%= t(".opening") %>
+<p><%= t(".opening") %></p>
 
-<%= edit_user_password_url(@user, token: @user.confirmation_token.html_safe) %>
+<p>
+  <%= link_to t(".link_text", default: "Change my password"),
+    edit_user_password_url(@user, token: @user.confirmation_token.html_safe) %>
+</p>
 
-<%= raw t(".closing") %>
+<p><%= raw t(".closing") %></p>

config/locales/clearance.en.yml

@@ -4,6 +4,7 @@ en:
     change_password:
       closing: If you didn't request this, ignore this email. Your password has
         not been changed.
+      link_text: Change my password
       opening: "Someone, hopefully you, requested we send you a link to change
         your password:"
   flashes:

spec/mailers/clearance_mailer_spec.rb

@@ -29,6 +29,9 @@
     email = ClearanceMailer.change_password(user)
 
     expect(email.body.to_s).to include(link)
+    expect(email.body.to_s).to have_css(
+      "a", text: I18n.t("clearance_mailer.change_password.link_text")
+    )
   end
 
   it "sets its subject" do