chore: update replica to 0.5.7 (#624)

This fixes an issue with principal being changed during a consensus round,
which was cherry picked on top of 0.5.6.

Author: Hans

nix/sources.json

@@ -32,9 +32,9 @@
         "type": "git"
     },
     "dfinity": {
-        "ref": "v0.5.6",
+        "ref": "v0.5.7",
         "repo": "ssh://[email protected]/dfinity-lab/dfinity",
-        "rev": "c2445f9aa8cf16dd29aabf2c47c2a5f3c870ee76",
+        "rev": "eb653572373754564ac815cd0785c5f7b9674d6d",
         "type": "git"
     },
     "ic-ref": {