NginxVersionRange from_native and from_string generating different VersionRange #24

>>> from univers.version_range import NginxVersionRange
>>> rng_from_native = NginxVersionRange.from_native("1.9.5-1.17.2")
>>> rng_from_string = NginxVersionRange.from_string(rng_from_native.to_string())
>>>
>>> assert rng_from_native == rng_from_string
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-65-c0fc3fe00843> in <module>
----> 1 assert rng_from_native == rng_from_string

AssertionError:
>>>
>>> rng_from_native.to_string()
'vers:nginx/>=1.9.5|<=1.17.2'
>>> rng_from_string.to_string()
'vers:nginx/>=1.9.5|<=1.17.2'


>>> rng_from_native
NginxVersionRange(constraints=(VersionConstraint(comparator='>=', version=Version('1.9.5')), VersionConstraint(comparator='<=', version=Version('1.17.2'))))

>>> rng_from_string
NginxVersionRange(constraints=(VersionConstraint(comparator='>=', version=SemverVersion(string='1.9.5')), VersionConstraint(comparator='<=', version=SemverVersion(string='1.17.2'))))
>>>