0.12.0-alpha regression: if no target is specified, dbt should use a target called "default"

[drewbanin]

Issue

A regression in the 0.12.0 alpha no longer uses the default target if a target: is not specified.

Issue description

Given a profile like:

{
    default: {
        outputs: {
            default: {
                type: 'postgres',
                threads: 1,
                host: 'localhost',
                port: 5432,
                user: 'root',
                pass: 'password',
                dbname: 'test',
                schema: 'test'
            }
        }
    }
}

(Note: There is no target specified here). Previous versions would use the "default" target if no target was listed explicitly. It looks like the alpha instead fails with:

Encountered an error while reading profiles:
  ERROR Runtime Error
  target not specified in profile 'default'

System information

The output of dbt --version:

0.12.0-a1

The operating system you're running on:
3.7