Unit tests fail on macOS

[dhonsel]

The CodonEvoTest.CodonEvoRateReadWrite test currently fails on macOS:

[ RUN      ] CodonEvoTest.CodonEvoRateReadWrite
codonevo_unittest.cc:55: Failure
The difference between gsl_matrix_get(Q0, 0, 0) and -1.11186 is 0.38031300000000012, which exceeds 1e-6, where
gsl_matrix_get(Q0, 0, 0) evaluates to -0.73154699999999995,
-1.11186 evaluates to -1.1118600000000001, and
1e-6 evaluates to 9.9999999999999995e-07.
codonevo_unittest.cc:56: Failure
The difference between gsl_matrix_get(Q2, 0, 1) and 0.07978618 is 0.026740819999999998, which exceeds 1e-6, where
gsl_matrix_get(Q2, 0, 1) evaluates to 0.106527,
0.07978618 evaluates to 0.079786179999999998, and
1e-6 evaluates to 9.9999999999999995e-07.
[  FAILED  ] CodonEvoTest.CodonEvoRateReadWrite (8 ms)