lamp-generic: lamp-edge branch is gone

@rafael says:

    Use master instead.

    nexedi/slapos@000d0e5a (comment 4716)

So lamp-edge -> master

software/unstable/lamp-generic/development.cfg

@@ -29,7 +29,7 @@ git-executable = ${git:location}/bin/git
 [slapos.cookbook-repository]
 recipe = slapos.recipe.build:gitclone
 repository = https://lab.nexedi.com/nexedi/slapos.git
-branch = lamp-edge
+branch = master
 git-executable = ${git:location}/bin/git
 
 [slapos.core-repository]