Update git submodules

* Update swift from branch 'master'
  - Merge "Add slo_manifest_hook callback"
  - Add slo_manifest_hook callback
    
    ... to allow other middlewares to impose additional constraints on
    or make edits to SLO manifests before being written.
    
    The callback takes a single argument: the python list that represents
    the manifest to be written. All the normal list operations listed at
    https://docs.python.org/2/library/stdtypes.html#mutable-sequence-types
    are available to make changes to that before SLO serializes it as JSON.
    
    The callback may return a list of problematic segments; each item in the
    list should be a tuple of
    
        (quoted object name, description of problem)
    
    This will be useful both for s3api minimum segment size validation and
    creating tar large objects.
    
    Change-Id: I198c5196e0221a72b14597a06e5ce3c4b2bbf436
    Related-Bug: #1636663

swift

@@ -1 +1 @@
-Subproject commit b25c88eb25686d91d338dbc194d709ea9e06c5df
+Subproject commit 4781b80b1ca26d977e8a731ffe63e689b2e4338c