build: rename _toc to toc (#654)

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Source-Link: googleapis/synthtool@99c93fe

packages/google-cloud-dialogflow/synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/nodejs-dialogflow.git",
-        "sha": "df7c60713e39dca5188c505975511f918a0f1209"
+        "sha": "ab01f56885023219312cc7bf501ca41e2694627b"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "21f1470ecd01424dc91c70f1a7c798e4e87d1eec"
+        "sha": "99c93fe09f8c1dca09dfc0301c8668e3a70dd796"
       }
     }
   ],