cygwinでgemが失敗

症状

$ gem update Updating installed gems ERROR: While executing gem .. (ArgumentError) invalid byte sequence in UTF-8

1 2 3 4

$ gem update Updating installed gems ERROR:  While executing gem .. (ArgumentError)     invalid byte sequence in UTF-8

回避策

$ LANG=C.BINARY gem update

1	$ LANG=C.BINARY gem update

$ LANG=C.BINARY gem install thread

1	$ LANG=C.BINARY gem install thread