correct pragma pop

[BorisMansencal]

Thanks a lot for contributing to DGtal, before submitting your PR, please fill up the description and make sure that all checkboxes are checked. Please remove these lines in your PR.

PR Description

Correct small error: the pragma pop was outside the if/endif block.

Checklist

• Unit-test of your feature with Catch.
• Doxygen documentation of the code completed (classes, methods, types, members...)
• Documentation module page added or updated.
• New entry in the ChangeLog.md added.
• No warning raised in Debug cmake mode (otherwise, Travis C.I. will fail).
• All continuous integration tests pass (Travis & appveyor)

[dcoeurjo]

correct... thanks. merging;)