fix(email) (#5373) r=@shane-tomlinson

Making the button match the call-to-action in the heading

app/scripts/templates/index.mustache

@@ -25,7 +25,7 @@
       </div>
 
       <div class="button-row">
-        <button id="submit-btn" type="submit" class="disabled">{{#t}}Next{{/t}}</button>
+        <button id="submit-btn" type="submit" class="disabled">{{#t}}Continue{{/t}}</button>
       </div>
     </form>
   </section>