test-models: added a 2x factor on the preciseness of the test to fail less
test-models: added a 2x factor on the preciseness of the test to fail less

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