Moved code to /src folder

src/models/variable-model.js

@@ -0,0 +1,12 @@
+const bookshelf = require('../database/bookshelf').bookshelf;
+
+require('./spell-model');
+
+let Variable = bookshelf.Model.extend({
+    tableName: 'variable',
+    spells() {
+        return this.belongsToMany('Spell', 'spell_variable');
+    }
+});
+
+module.exports = bookshelf.model('Variable', Variable);