Test failure when building with MKL

[peddie]

albatross/tests/test_sparse_gp.cc:405: Failure
Expected: ((direct_pred.covariance - iter_pred.covariance).norm()) < (1e-5), actual: 1.53745e-05 vs 1e-05
[  FAILED  ] SparseGaussianProcessTest/0.test_rebase_and_update, where TypeParam = albatross::LeaveOneIntervalOut (0 ms)

Not reassuring to encounter subtle numerical differences like this.