Replace "execute_script" for filling in Close Account modal

Using "fill_in" seems to work fine with the apparition driver, and will hopefully also work on CI now.

features/step_definitions/modal_steps.rb

@@ -9,9 +9,7 @@ Then /^I should see the mention modal$/ do
 end
 
 When /^I put in my password in the close account modal$/ do
-  # Capybara helpers fill_in, set and send_keys currently don't work
-  # inside of Bootstrap modals on Travis CI
-  execute_script("$(\"#closeAccountModal input#close_account_password\").val(\"#{@me.password}\")")
+  fill_in("#close_account_password", with: @me.password)
   expect(find("#closeAccountModal input#close_account_password").value).to eq(@me.password)
 end