chore: make Experiment.AutoFixture.nuspec

- resolve nuget dependency verioning
fix: fix transform file extention (.cs.pp).
docs: fix word spacing.
fix: fix using derctives

when installing the source codes, necessary namespace is not declared
as-is.
chore(release): increment pre-release version,

to indicate that this is to test that Experiment.AutoFixture is pushed
to nuget sever and user can install it correctly.