Test data from FSL 5.0.10 has been merged

[cmaumet]

What does this PR do?

Fix error identified in https://github.com/incf-nidash/nidmresults-fsl/issues/149.

Possible reason: Travis tests are failing because the branch containing test data 'fsl_5.0.10' is not found is the test data repository as it has been merged (master should be used as target branch instead).

Link to relevant issues

https://github.com/incf-nidash/nidmresults-fsl/issues/149, https://github.com/incf-nidash/nidmresults-fsl/pull/146, https://github.com/incf-nidash/nidmresults-fsl/pull/147.

PR submission checklist

• [x] All tests in the test suite pass
• [x] Tick when PR is ready for review (i.e. not work-in-progress)