[CLI] DATABASE_URL shouldn't be necessary for simple commands

[c410-f3r]

$ sqlx -V
Error: Failed to find 'DATABASE_URL'

Caused by:
    environment variable not found

[abonander]

Probably closed by #249, @c410-f3r can you update your clone and run cargo install -f --path sqlx-cli

[c410-f3r]

Not anymore! Thanks for fixing it!