Linter: Fix all lint errors

Signed-off-by: Philip Molares <philip.molares@udo.edu>

lib/models/author.js

@@ -1,9 +1,9 @@
 'use strict'
 // external modules
-var Sequelize = require('sequelize')
+const Sequelize = require('sequelize')
 
 module.exports = function (sequelize, DataTypes) {
-  var Author = sequelize.define('Author', {
+  const Author = sequelize.define('Author', {
     id: {
       type: Sequelize.INTEGER,
       primaryKey: true,