Switch from node-mariasql to mysql2

Node-mariasql returned dates in an incorrect timezone, and the project
doesn't seem to be actively maintained. Switching to mysql2 fixes the issue.

knexfile.js

@@ -1,19 +1,23 @@
 require('dotenv').config();
 
+const moment = require('moment-timezone');
+moment.tz.setDefault('UTC');
+
 module.exports = {
-  client: 'mariasql',
+  client: 'mysql2',
   connection: {
     host: process.env.DB_HOST,
     user: process.env.DB_USER,
     password: process.env.DB_PASSWORD,
-    db: process.env.DB_DATABASE,
-    charset: 'utf8mb4'
-  },
-  pool: {
-    afterCreate(connection, callback) {
-      connection.query("SET time_zone = '+0:00';", err => {
-        callback(err, connection);
-      });
+    database: process.env.DB_DATABASE,
+    charset: 'utf8mb4',
+    timezone: 'UTC',
+    typeCast(field, next) {
+      if (field.type === 'DATETIME') {
+        return moment(field.string()).format('YYYY-MM-DD HH:mm:ss');
+      }
+
+      return next();
     }
   }
 };