core/loginuserpass: Fix login button translation (#1332)

Fixes 336b7abe which changed the label from
'Login' to a single-use 'Log in' whilste the translations only have 'Login'.

modules/core/templates/loginuserpass.twig

@@ -114,7 +114,7 @@
 
             <button class="pure-button pure-button-red pure-input-1-2 pure-input-sm-1-1 right" id="submit_button"
                     type="submit" tabindex="6" data-processing="{% trans %}Processing...{% endtrans %}">
-              {% trans %}Log in{% endtrans %}
+              {% trans %}Login{% endtrans %}
             </button>
         </form>
     </div><!--center-->