`node_transaction_history_pkey` is missing

[bitjson]

Somehow I lost node_transaction_history_pkey before release, so the node_transaction_history table has no primary key. That will become an issue after Chaingraph is running for a little while, since most node_transaction_history queries will require a full table scan.

In the next migration we need to add:

ALTER TABLE ONLY node_transaction_history
  ADD CONSTRAINT node_transaction_history_pkey PRIMARY KEY (internal_id);

(And maybe in the next major version we can squash all schema changes back into a single file? That would really just be for aesthetics, Hasura manages migrations very well.)