Add nginx 1.15.7, remove nginx 1.15.6
Add nginx 1.15.7, remove nginx 1.15.6

for stack(s) cflinuxfs2, cflinuxfs3 [#162240857]

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