Password env var name

[willbryant]

Not clear what the env var should be called. Readme and first place in the code says MB_PASS:

ENV_VARS = [
    "DBT_DATABASE",
    "DBT_PATH",
    "DBT_MANIFEST_PATH",
    "MB_USER",
    "MB_PASS",

But the actual env var handling code says:

    "DBT_PATH",
    "DBT_MANIFEST_PATH",
    "MB_USER",
    "MB_PASS",

    @click.option(
        "--metabase_password",
        metavar="PASS",
        envvar="MB_PASSWORD",

Is the latter wrong?

[gouline]

Not sure either one even works, they seem to exclude each other. It should be MB_PASSWORD if you feel like doing a quick PR.