GM: now that we use MD5 instead of CityHash, the JSON should say so

gm/tests/outputs/compared-against-empty-dir/output-expected/json-summary.txt

Index: gm/tests/outputs/compared-against-empty-dir/output-expected/json-summary.txt
===================================================================
--- gm/tests/outputs/compared-against-empty-dir/output-expected/json-summary.txt	(revision 8994)
+++ gm/tests/outputs/compared-against-empty-dir/output-expected/json-summary.txt	(working copy)
@@ -4,21 +4,21 @@
       "failure-ignored" : null,
       "no-comparison" : {
          "565/selftest1" : {
-            "bitmap-cityhash" : 12927999507540085554
+            "bitmap-64bitMD5" : 12927999507540085554
          },
          "8888/selftest1" : {
-            "bitmap-cityhash" : 1209453360120438698
+            "bitmap-64bitMD5" : 1209453360120438698
          }
       },
       "succeeded" : null
    },
    "expected-results" : {
       "565/selftest1" : {
-         "allowed-bitmap-cityhashes" : null,
+         "allowed-bitmap-64bitMD5s" : null,
          "ignore-failure" : false
       },
       "8888/selftest1" : {
-         "allowed-bitmap-cityhashes" : null,
+         "allowed-bitmap-64bitMD5s" : null,
          "ignore-failure" : false
       }
    }