v0.9.0

Enhancements:

• jill now discards the slow version query mechanism and uses the Julia officially maintained versions.json file (#58) (@crstnbr)
• The environment variable JILL_UPSTREAM works the same as jill cmd --upstream; you can predefine the upstream so as to avoid typing --upstream flag again and again. (#61)(@crstnbr)
• jill now supports some os/arch alias. For example, jill download --sys win is a valid option now. (#62)(@johnnychen94)
• By default, jill mirror will also download test releases (e.g., alpha/beta/rc) (#62)(@johnnychen94)

Breaking changes:

• jill update no longer exists (#58)(@crstnbr)