bump version to 0.4.0b4
bump version to 0.4.0b4

jerkos/cobrapy,jeicher/cobrapy,zakandrewking/cobrapy,aebrahim/cobrapy,aebrahim/cobrapy,zakandrewking/cobrapy,JuBra/cobrapy,jerkos/cobrapy,jeicher/cobrapy,JuBra/cobrapy