Update to polynomial.py
Update to polynomial.py

Edited the documentation of polyfit.
The scaling factor of the covariance matrix in the description was erroneous, the correct form is chi2/dof. 
The code already used this correct scaling, just the description needed to be updated.
jakirkham/numpy,anntzer/numpy,endolith/numpy,grlee77/numpy,numpy/numpy,grlee77/numpy,mhvk/numpy,mhvk/numpy,grlee77/numpy,charris/numpy,madphysicist/numpy,seberg/numpy,seberg/numpy,madphysicist/numpy,madphysicist/numpy,endolith/numpy,numpy/numpy,pbrod/numpy,jakirkham/numpy,rgommers/numpy,mattip/numpy,charris/numpy,madphysicist/numpy,rgommers/numpy,pbrod/numpy,pbrod/numpy,pdebuyl/numpy,seberg/numpy,charris/numpy,endolith/numpy,mhvk/numpy,rgommers/numpy,anntzer/numpy,mattip/numpy,seberg/numpy,jakirkham/numpy,anntzer/numpy,simongibbons/numpy,pdebuyl/numpy,jakirkham/numpy,simongibbons/numpy,numpy/numpy,anntzer/numpy,madphysicist/numpy,pdebuyl/numpy,endolith/numpy,simongibbons/numpy,pdebuyl/numpy,mhvk/numpy,jakirkham/numpy,mattip/numpy,mattip/numpy,mhvk/numpy,pbrod/numpy,pbrod/numpy,numpy/numpy,simongibbons/numpy,charris/numpy,grlee77/numpy,grlee77/numpy,simongibbons/numpy,rgommers/numpy