Changed some more instances of "confirmation" code to "security" code

app/templates/views/text-not-received.html

@@ -12,11 +12,11 @@ Check your mobile number – GOV.UK Notify
   <div class="column-two-thirds">
     <h1 class="heading-large">Check your mobile number</h1>
 
-    <p>Check your mobile phone number is correct and then resend the confirmation code.</p>
+    <p>Check your mobile phone number is correct and then resend the security code.</p>
 
       <form autocomplete="off" method="post">
         {{ textbox(form.mobile_number) }}
-        {{ page_footer("Resend confirmation code") }}
+        {{ page_footer("Resend security code") }}
       </form>
   </div>
 </div>