Add nginx 1.15.8, remove nginx 1.15.7
Add nginx 1.15.8, remove nginx 1.15.7

for stack(s) cflinuxfs2, cflinuxfs3 [#162839811]

cloudfoundry/staticfile-buildpack,cloudfoundry/staticfile-buildpack,cloudfoundry/staticfile-buildpack,cloudfoundry/staticfile-buildpack