fixed np->numpy in plfit.py as per issue 8
fixed np->numpy in plfit.py as per issue 8

tectronics/agpy,Leotrinos/agpy,jcesardasilva/agpy,ufoym/agpy,ufoym/agpy,tectronics/agpy,ufoym/agpy,jcesardasilva/agpy,Leotrinos/agpy,tectronics/agpy,jcesardasilva/agpy,Leotrinos/agpy,tectronics/agpy,jcesardasilva/agpy,Leotrinos/agpy,ufoym/agpy