Fix: fixed bug in tangle plugin when persisting approvers

packages/curl/batch_hasher.go

packages/model/approvers/approvers.go

packages/model/meta_transaction/constants.go

packages/model/meta_transaction/meta_transaction.go

packages/model/value_transaction/value_transaction.go

packages/model/valuebundle/metabundle.go

plugins/gossip/protocol_v1.go

plugins/gossip/transaction_processor_test.go

plugins/tangle/approvers.go

plugins/tangle/solidifier.go

plugins/tangle/transaction_metadata.go