v0.3.2-rc.7

Fix correct empty output for implicit in call.

v0.3.2-rc.6: Fix output of check and in calls.

The "check" and "in" calls now return the correct output that the
Concourse JSON parser expects (a list).

Moreover this commit fixes a bug appearing when the check is called:
Concourse does not pass any additional arguments and thus the reading
of the "workspace" value must be proteced otherwise Concourse displays
an error on the check resource.

v0.3.2-rc.5: Fix typo in error message when missing webhook_url.

Fix ATC complaining that resource.versionResult cannot be unmarshalled when the webhook_url parameter is empty/missing.