Increase unit test threshold for OS X.
Increase unit test threshold for OS X.

See failure: https://travis-ci.org/dhermes/bezier/builds/338354752

The error bound likely went up because matrix operations are
non-deterministic (i.e. they depend on the order the BLAS operations
are done in ) and we have transposed many of our matrices.

dhermes/bezier,dhermes/bezier,dhermes/bezier