Refactored smells out of query_runner/table_on_demand.rb

Smells reported by reek:

Before:

 1: NoBrainer::QueryRunner::TableOnDemand has no descriptive comment
    (IrresponsibleModule)
 5: NoBrainer::QueryRunner::TableOnDemand#call has the variable name
    'e' (UncommunicativeVariableName)

After:

 1: NoBrainer::QueryRunner::TableOnDemand has no descriptive comment
    (IrresponsibleModule)

Notes:

Just a trivial change (e -> err)