cglpk: bugfix to LP file writing with python 3
cglpk: bugfix to LP file writing with python 3

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