CI: fix Travis CI py3.8 build (#10918)
CI: fix Travis CI py3.8 build (#10918)

Switch py3.8 numpy to dev version. Previously, the build used some
Travis-supplied Numpy dev version, but it's useful to have control
over this.
tylerjereddy/scipy,endolith/scipy,e-q/scipy,scipy/scipy,WarrenWeckesser/scipy,tylerjereddy/scipy,tylerjereddy/scipy,perimosocordiae/scipy,pizzathief/scipy,arokem/scipy,mdhaber/scipy,matthew-brett/scipy,endolith/scipy,endolith/scipy,rgommers/scipy,person142/scipy,person142/scipy,nmayorov/scipy,andyfaff/scipy,mdhaber/scipy,pizzathief/scipy,Stefan-Endres/scipy,endolith/scipy,nmayorov/scipy,jamestwebber/scipy,matthew-brett/scipy,e-q/scipy,jor-/scipy,vigna/scipy,person142/scipy,Eric89GXL/scipy,rgommers/scipy,perimosocordiae/scipy,matthew-brett/scipy,endolith/scipy,WarrenWeckesser/scipy,anntzer/scipy,andyfaff/scipy,e-q/scipy,nmayorov/scipy,scipy/scipy,scipy/scipy,rgommers/scipy,zerothi/scipy,tylerjereddy/scipy,vigna/scipy,pizzathief/scipy,endolith/scipy,ilayn/scipy,arokem/scipy,WarrenWeckesser/scipy,andyfaff/scipy,arokem/scipy,mdhaber/scipy,zerothi/scipy,Stefan-Endres/scipy,andyfaff/scipy,rgommers/scipy,jamestwebber/scipy,Eric89GXL/scipy,pizzathief/scipy,Stefan-Endres/scipy,Stefan-Endres/scipy,anntzer/scipy,aeklant/scipy,grlee77/scipy,Eric89GXL/scipy,anntzer/scipy,tylerjereddy/scipy,zerothi/scipy,grlee77/scipy,anntzer/scipy,scipy/scipy,matthew-brett/scipy,perimosocordiae/scipy,aeklant/scipy,aeklant/scipy,grlee77/scipy,e-q/scipy,grlee77/scipy,mdhaber/scipy,vigna/scipy,mdhaber/scipy,nmayorov/scipy,jamestwebber/scipy,andyfaff/scipy,ilayn/scipy,zerothi/scipy,vigna/scipy,WarrenWeckesser/scipy,Eric89GXL/scipy,ilayn/scipy,vigna/scipy,scipy/scipy,perimosocordiae/scipy,rgommers/scipy,perimosocordiae/scipy,perimosocordiae/scipy,jor-/scipy,Stefan-Endres/scipy,jor-/scipy,arokem/scipy,zerothi/scipy,andyfaff/scipy,WarrenWeckesser/scipy,WarrenWeckesser/scipy,aeklant/scipy,scipy/scipy,Stefan-Endres/scipy,aeklant/scipy,matthew-brett/scipy,anntzer/scipy,ilayn/scipy,Eric89GXL/scipy,jor-/scipy,person142/scipy,Eric89GXL/scipy,nmayorov/scipy,ilayn/scipy,pizzathief/scipy,zerothi/scipy,jor-/scipy,e-q/scipy,jamestwebber/scipy,mdhaber/scipy,ilayn/scipy,arokem/scipy,grlee77/scipy,anntzer/scipy,person142/scipy,jamestwebber/scipy