nix/sources.json: upgrade common the get the latest nixpkgs 19.09
"common": {
"ref": "master",
"repo": "ssh://git@github.com/dfinity-lab/common",
- "rev": "16b88b24e34e9f766e32804af50d16d93a48fd2c",
+ "rev": "ae308ce927bc2128b704b74041ea18913c8313bb",
"type": "git"
},
"dfinity": {
