Create db dir if it doesn't exist

.dockerignore

@@ -3,4 +3,4 @@ log
 node_modules
 samples
 sessions
-db.sqlite3
+db

server/db.js

@@ -1,3 +1,7 @@
 const sqlite3 = require('sqlite3')
+const fs = require('fs')
 
+if (!fs.existsSync('db')) {
+  fs.mkdirSync('db')
+}
 module.exports = new sqlite3.Database('db/db.sqlite3')