Fix a doc-comment
Fix a doc-comment

The `store` in a handler is a generic DataStore, not just an events.StateStore.

matrix-org/synapse,TribeMedia/synapse,matrix-org/synapse,TribeMedia/synapse,matrix-org/synapse,TribeMedia/synapse,TribeMedia/synapse,TribeMedia/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse