Catch CleanupS3 error (> 1000 objects)

[johanlef]

Running s3Sync.syncCleanInvalidate() on a bucket containing more than 1000 objects:

UnhandledPromiseRejectionWarning: Error: Bucket contains more than 1.000 objects, operation currently not supported
    at cleanupS3 (~/Sites/e-learning/client/node_modules/s3-sync/lib/cleanupS3.js:29:11)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
    at async Object.syncCleanInvalidate (~/Sites/e-learning/client/node_modules/s3-sync/lib/index.js:20:15)
(node:64668) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:64668) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.