Include correct validation error with username invalid.

app/views/devise/shared/_signup_box.html.haml

@@ -8,8 +8,7 @@
         = f.text_field :name, class: "form-control top", required: true, title: "This field is required."
       %div.username.form-group
         = f.label :username
-        = f.text_field :username, class: "form-control middle no-gl-field-error", pattern: "[a-zA-Z0-9]+", required: true
-        %p.gl-field-error.hide Please create a username with only alphanumeric characters.
+        = f.text_field :username, class: "form-control middle no-gl-field-error", pattern: "[a-zA-Z0-9]+", required: true, title: 'Please create a username with only alphanumeric characters.'
         %p.validation-error.hide Username is already taken.
         %p.validation-success.hide Username is available.
         %p.validation-pending.hide Checking username availability...