Allow big integer values for Toggl ID

As Toggl IDs get bigger, Redmine tables need to be able to accomodate them.

Author: jigarius

db/migrate/005_change_toggl_mappings_toggl_id_to_bigint.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class ChangeTogglMappingsTogglIdToBigint < ActiveRecord::Migration[4.2]
+  def up
+    change_column :toggl_mappings, :toggl_id, :bigint
+  end
+end