Tests fail because of non-deterministic floating-point precision #62

If I run pytest I get failures because of a what appears to be due to difference in precision in the time= attribute in the xml

What's expected

<testsuites disabled="0" errors="0" failures="24" tests="65" time="0.019785572146">

What I get

<testsuites disabled="0" errors="0" failures="24" tests="65" time="0.019785572145999998">

I suspect this is due to different behaviors in the underlying yamlish and PyYAML dependencies on different platforms.

I don't think it's a big deal that floating-point conversion of TAP to JUnit is non-deterministic on different platforms.
But it's regrettable that the tests of tap2junit relies on this deterministic behavior.

I'm going to take a look and see if I can fix this in a suitable manner, meanwhile I report the issue here.