[BUG]phpcpd is being invoked incorrectly

[alxp]

What steps does it take to reproduce the issue?

Found when automated testing is run against this PR: Islandora/islandora_defaults#75

• When does this issue occur?

When phpcpd is invoked on a module that contains no "*.php" files.

• What happens?

Build failure.

• To whom does it occur (anonymous visitor, editor, administrator)?

Github robot.

• What did you expect to happen?

All jobs should run successfully since no new code was added.

Which version of Islandora are you using?

2.x

Any related open or closed issues to this bug report?

Islandora/islandora_defaults#75

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