Proposed changes

On ocean, update Catch to meet the new requirement of >= 2.8.

Types of changes:

• Bugfix
• New feature
• Refactor

Component:

• Code
• Documentation
• Build system
• Continuous integration

Code review checklist

• The PR passes all checks, including unit tests and clang-tidy.
  For instructions on how to perform the CI checks locally refer to the Dev
  guide on the Travis CI.
• The code is documented and the documentation renders correctly. Run
  make doc to generate the documentation locally into BUILD_DIR/docs/html.
  Then open index.html.
• The code follows the stylistic and code quality guidelines listed in the
  code review guide.

Further comments