message: [small] Expose json rpc error enum
  Closes:
  Approved by: thefallentree
diff: @@ -7,7 +7,8 @@ mod response;
  pub use blocking::JsonRpcClient;
  pub use client::{
  - get_response_from_batch, process_batch_response, JsonRpcAsyncClient, JsonRpcBatch,
  + get_response_from_batch, process_batch_response, JsonRpcAsyncClient, JsonRpcAsyncClientError,
  + JsonRpcBatch,
  };
  pub use libra_json_rpc_types::{errors, views};
  pub use libra_types::{account_address::AccountAddress, transaction::SignedTransaction};
  