fix: add missing head -n1 call to second build-env test
fix: add missing head -n1 call to second build-env test

Otherwise `docker inspect` outputs a "condensed" json output that doesn't parse as well...
jimjag/dokku,progrium/dokku,dokku/dokku,alexquick/dokku,dokku/dokku,alexquick/dokku,jimjag/dokku,jimjag/dokku,alexquick/dokku,jimjag/dokku,dokku/dokku,alexquick/dokku,progrium/dokku,claytonbrown/dokku,jimjag/dokku,claytonbrown/dokku,dokku/dokku,dokku/dokku,progrium/dokku,alexquick/dokku,claytonbrown/dokku,alexquick/dokku,jimjag/dokku,progrium/dokku,claytonbrown/dokku,claytonbrown/dokku,jimjag/dokku,jimjag/dokku,dokku/dokku,progrium/dokku,progrium/dokku,progrium/dokku,dokku/dokku,claytonbrown/dokku,alexquick/dokku,claytonbrown/dokku,dokku/dokku,progrium/dokku,claytonbrown/dokku,alexquick/dokku