missing backslash in dockerfile

https://github.com/aws-samples/aws-batch-using-nice-dcv/blob/75459f56fb9ff1ec426e50a2b89e35cc0c96d6e7/aws-batch-using-nice-dcv.dockerfile#L73

Open aws-batch-using-nice-dcv.dockerfile and inspect line 73, where the issue identifies a missing backslash. Confirm the Dockerfile syntax and surrounding command continuation, then verify that the corrected file builds successfully.

Written by the indexing model from the issue text.