Performance issues in the programs

[DLPerf]

Hello,I found a performance issue in rishizek/tensorflow-deeplab-v3-plus/blob/master/utils/dataset_util.py ,dataset.interleave
was called without num_parallel_calls.I think it will increase the efficiency of your program if you add this.
Here is the documemtation of tensorflow to support this thing.

Looking forward to your reply. Btw, I am very glad to create a PR to fix it if you are too busy.