Eric Semeniuc abb71120f0 Fixes migration macro with no params
Fixes issue experienced in https://github.com/launchbadge/sqlx/issues/746 when using no parameter:

```
error: paths relative to the current file's directory are not currently supported
 --> src/db.rs:7:5
  |
7 |     sqlx::migrate!().run(&conn).await?;
  |     ^^^^^^^^^^^^^^^^
  |
  = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
```
2020-10-22 21:48:57 -07:00
..
2020-10-22 21:48:57 -07:00