Cache commit's author and committer when indexing a commit

... as these data are not cached in rugged.

lib/elasticsearch/git/repository.rb

@@ -217,6 +217,9 @@ module Elasticsearch
         end
         def index_commit(commit)
+          author    = commit.author
+          committer = commit.committer
+
           {
             index:  {
               _index: "#{self.class.index_name}",
@@ -229,14 +232,14 @@ module Elasticsearch
                   rid: repository_id,
                   sha: commit.oid,
                   author: {
-                    name: encode!(commit.author[:name]),
-                    email: encode!(commit.author[:email]),
-                    time: commit.author[:time].strftime('%Y%m%dT%H%M%S%z'),
+                    name: encode!(author[:name]),
+                    email: encode!(author[:email]),
+                    time: author[:time].strftime('%Y%m%dT%H%M%S%z'),
                   },
                   committer: {
-                    name: encode!(commit.committer[:name]),
-                    email: encode!(commit.committer[:email]),
-                    time: commit.committer[:time].strftime('%Y%m%dT%H%M%S%z'),
+                    name: encode!(committer[:name]),
+                    email: encode!(committer[:email]),
+                    time: committer[:time].strftime('%Y%m%dT%H%M%S%z'),
                   },
                   message: encode!(commit.message)
                 }