FFEA cannot build because Eigen Bitbucket repo is broken.

[Ryan Cocking]

Eigen migrated to GitLab on 30/07/2020, but it would appear they have now deleted the original Bitbucket repo. FFEA is unable to build from source due to a download error.

Broken URL: https://bitbucket.org/eigen/eigen/get/3.3.4.tar.bz2
GitLab URL: https://gitlab.com/libeigen/eigen.git

I have tried updating the URL in cmake/GetEigen3.cmake, but I am unsure what the URL_HASH should be to avoid getting a hash mismatch error when attempting to build again.

[Ryan Cocking]

Fixed by replacing the relevant fields in cmake/GetEigen3.cmake with the latest stable Eigen release on Gitlab and the result from running sha256sum eigen-3.3.7.tar.gz in the terminal.