Fix test that fails on Windows
The test with model
fluH3N2_deepMutScanFitnessBD_sub2009-2012_67muts_addLog2SFit.xml
failed on Windows because some of the numerical results were different,
albeit within machine precision. Instead of a string comparison between
the log and reference, we now compare the actual numbers on the last
line with a relative tolerance of 1e-15.