fixed typo in test/unit-agrad-rev/nan_util
fixed typo in test/unit-agrad-rev/nan_util

stan-dev/stan,stan-dev/stan,stan-dev/math,stan-dev/stan,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math