1.0.0a6

• dvcignore: fix bug in subrepo detection (#3880) @efiop
• run: raise error when command is not specified (#3850) @skshetry
• ignore: CleanTree should always check ignores, not just for walk() (#3876) @pmrowla
• addressing: allow stage name addressing without ":" (#3842) @skshetry
• run-cache: don't forget to set wdir (#3873) @efiop
• state: always use working trees (#3871) @pmrowla
• log: reduce log, make it readable/easier (#3834) @skshetry