TST: Add 3.9-dev to the travis matrix
TST: Add 3.9-dev to the travis matrix

Co-authored-by: Charles Harris <c6ce714bfdf426eed9ce131deb8d469a944b83b9@gmail.com>

jakirkham/numpy,jakirkham/numpy,pdebuyl/numpy,anntzer/numpy,simongibbons/numpy,rgommers/numpy,endolith/numpy,rgommers/numpy,simongibbons/numpy,pbrod/numpy,anntzer/numpy,grlee77/numpy,madphysicist/numpy,abalkin/numpy,pdebuyl/numpy,seberg/numpy,mattip/numpy,abalkin/numpy,madphysicist/numpy,anntzer/numpy,madphysicist/numpy,pdebuyl/numpy,simongibbons/numpy,mattip/numpy,abalkin/numpy,endolith/numpy,simongibbons/numpy,grlee77/numpy,jakirkham/numpy,numpy/numpy,rgommers/numpy,charris/numpy,simongibbons/numpy,charris/numpy,seberg/numpy,mhvk/numpy,madphysicist/numpy,endolith/numpy,numpy/numpy,charris/numpy,mattip/numpy,charris/numpy,pdebuyl/numpy,numpy/numpy,rgommers/numpy,anntzer/numpy,mhvk/numpy,mattip/numpy,grlee77/numpy,seberg/numpy,grlee77/numpy,seberg/numpy,pbrod/numpy,jakirkham/numpy,grlee77/numpy,numpy/numpy,mhvk/numpy,mhvk/numpy,pbrod/numpy,madphysicist/numpy,mhvk/numpy,endolith/numpy,jakirkham/numpy,pbrod/numpy,pbrod/numpy