Unify the batch span processor parameters (#708)
Unify the batch span processor parameters (#708)

The parameter `maxExportBatchSize` refers to "export", but
`exporterTimeoutMillis` refers to the "exporter." This unifies on
"export" since they are both in reference to the same process.
open-telemetry/opentelemetry-specification,open-telemetry/opentelemetry-specification