Ignore additional build directory #51

Job	Run time
Linux build (openblas)	4m 28s
Linux build (openblas / static)	6m 46s
Linux build (mkl)	5m 52s
Mac build (accelerate / static)	3m 41s
Windows build (mkl)	4m 33s
Windows build (openblas)	3m 30s
Windows build openblas installed (mkl)	5m 11s
Mac build (accelerate)	1m 59s
	36m 0s

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