fix style issues

lib/memex/accounts/user.ex

@@ -140,7 +140,7 @@ defmodule Memex.Accounts.User do
     |> cast(attrs, [:email])
     |> validate_email()
     |> case do
-      %{changes: %{email: _}} = changeset -> changeset
+      %{changes: %{email: _email}} = changeset -> changeset
       %{} = changeset -> add_error(changeset, :email, dgettext("errors", "did not change"))
     end
   end

lib/memex/accounts/user_token.ex

@@ -155,7 +155,7 @@ defmodule Memex.Accounts.UserToken do
     from t in __MODULE__, where: t.user_id == ^user.id
   end
 
-  def user_and_contexts_query(user, [_ | _] = contexts) do
+  def user_and_contexts_query(user, [_head | _rest] = contexts) do
     from t in __MODULE__, where: t.user_id == ^user.id and t.context in ^contexts
   end
 end