use local time instead of UTC, migrate.js, closes #131

Run `node migrate.js localtime data/*.json` to convert
existing `time` entries from UTC to your local timezone.

migrate.js

@@ -0,0 +1,34 @@
+import { existsSync } from 'fs';
+import { Low } from 'lowdb';
+import { JSONFile } from 'lowdb/node';
+import { datetime } from './util.js';
+
+const datetime_UTCtoLocalTimezone = async file => {
+  if (!existsSync(file))
+    return console.error('File does not exist:', file);
+  const db = new Low(new JSONFile(file));
+  await db.read();
+  db.data ||= {};
+  console.log('Migrating', file);
+  for (const user in db.data) {
+    for (const game in db.data[user]) {
+      const time1 = db.data[user][game].time;
+      const time1s = time1.endsWith('Z') ? time1 : time1 + ' UTC';
+      const time2 = datetime(new Date(time1s));
+      console.log([game, time1, time2]);
+      db.data[user][game].time = time2;
+    }
+  }
+  // console.log(db.data);
+  await db.write(); // write out json db
+};
+
+const args = process.argv.slice(2);
+if (args[0] == 'localtime') {
+  const files = args.slice(1);
+  console.log('Will convert UTC datetime to local timezone for', files);
+  files.forEach(datetime_UTCtoLocalTimezone);
+} else {
+  console.log('Usage: node migrate.js <cmd> <args>');
+  console.log('       node migrate.js localtime data/*.json');
+}