Upgrade composer to 0.4.0

[lct8712]

Composer has released 0.4.0:
https://github.com/gojuno/composer/releases
Maybe upgrade the default version in gradle plugin from 0.3.0 to 0.4.0.

[Trevor Jones]

composer is selected via normal gradle dependency management via the 'composer' configuration on which ever project a task/plugin is applied so you can override the behavior.

once we get #28 merged i'll put out a new version with everything bumped to latest stable all around. really 28 is pre-req to usable orchestrator support anyway.

[Trevor Jones]

try 0.9.0