Update/deployment calls may panic because no receipt

[geigerzaehler]

It is possible that calls to functions that submit transactions panic if the transaction is not applied quickly enough. Calls that are affected are the ledger deployment and any ledger updates.

So far, this problem has only occurred with concurrent ledger deployments in the tests. It is likely that the problem only occurs when computation/storage-heavy transaction are submitted concurrently.

The issue is caused by tomusdrw/rust-web3#256.