bump_prerelease and bump_build return smaller version #221
Description
The current behavior of bump_prerelease and bump_build seems wrong, or at least unexpected:
In [64]: v1 = semver.parse_version_info('0.1.4')
In [65]: v1 < v1.bump_major() # good
Out[65]: True
In [66]: v1 < v1.bump_minor() # good
Out[66]: True
In [67]: v1 < v1.bump_patch() # good
Out[67]: True
In [68]: v1 < v1.bump_prerelease() # not good
Out[68]: False
In [69]: v1 < v1.bump_build() # not good
Out[69]: False
Is this deliberate? I would expect them to return what v1.bump_patch().bump_prerelease() and v1.bump_patch().bump_build() return now.