Update after the review

Author: xuniq

doc/dev_guide/internals/iproto/images/repl_heartbeat_message.puml

@@ -12,7 +12,9 @@ json "**Heartbeat message from master**" as heartbeat_request {
     "Header": {
       "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys/#general IPROTO_REQUEST_TYPE]]": "IPROTO_OK",
       "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys/#general-replication IPROTO_REPLICA_ID]]": "MP_UINT",
-      "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys/#general IPROTO_TIMESTAMP]]": "MP_DOUBLE",
+      "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys/#general IPROTO_TIMESTAMP]]": "MP_DOUBLE"
+    },
+    "Body": {
       "(Optional) [[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys/#general-replication IPROTO_VCLOCK_SYNC]]": "MP_UINT"
     }
 }

doc/dev_guide/internals/iproto/images/repl_heartbeat_message.svg

@@ -16,7 +16,7 @@ json "**Response from replica**" as heartbeat_response {
     },
     "Body": {
       "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys/#general-replication IPROTO_VCLOCK]]": "MP_MAP",
-      "(Optional) [[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys/#general IPROTO_VCLOCK_SYNC]]": "MP_UINT",
+      "(Optional) [[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys/#general-replication IPROTO_VCLOCK_SYNC]]": "MP_UINT",
       "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys/#synchronous-replication IPROTO_TERM]]": "MP_UINT"
     }
 }