fix: support passing file:// URI when SQLite was compiled with `SQLIT…

…E_USE_URI=1`

I'm trying to use `better-sqlite3` with an SQLite that is compiled with
`SQLITE_USE_URI=1`:

```js
const db = SQLite(`file:///foo/bar?vfs=myfs&mode=ro&immutable=1`);
```

This, however, doesn't work right now, since there's an erroneous
assertion in the database creation.

With this patch, I can successfully connect to database.

References WiseLibs#483

lib/database.js

@@ -61,7 +61,7 @@ function Database(filenameGiven, options) {
 	}
 
 	// Make sure the specified directory exists
-	if (!anonymous && !fs.existsSync(path.dirname(filename))) {
+	if (!filename.startsWith('file://') && !anonymous && !fs.existsSync(path.dirname(filename))) {
 		throw new TypeError('Cannot open database because the directory does not exist');
 	}