Fail to parse units defined with multiple prefixes
See https://github.com/olbrich/ruby-units/commit/07680c39704a7be158db8c27847e2fa869fff92a
Add mc as alternate definition for prefix "micro"
See https://github.com/olbrich/ruby-units/commit/f983da75c50a3521363f5d7f422b769dd447a840