fix(sign_in_code): fix code numeric input

Fixes #6765

app/scripts/templates/sign_in_token_code.mustache

@@ -15,7 +15,7 @@
 
     <form novalidate>
       <div class="input-row token-code-row">
-        <input type="number" class="tooltip-below token-code" placeholder="{{#t}}Enter code{{/t}}" required autofocus />
+        <input type="number" pattern="\d*" class="tooltip-below token-code" placeholder="{{#t}}Enter code{{/t}}" required autofocus />
       </div>
 
       <div class="button-row">