Update README.

Update the README with new docker container links for TF >= 2.3.0

Author: Amit Patankar

README.md

@@ -11,7 +11,7 @@ manylinux2010 compatible. To help you building custom ops on linux, here we prov
 | | CPU custom op | GPU custom op |
 |----------|:-------------------------------:|:------------------------------:|
 | TF nightly | nightly-custom-op-ubuntu16 | nightly-custom-op-gpu-ubuntu16 |
-| TF >= 2.1 | 2.1.0-custom-op-ubuntu16 | 2.1.0-custom-op-gpu-ubuntu16 |
+| TF >= 2.3 | 2.3.0-custom-op-ubuntu16 | 2.3.0-custom-op-gpu-ubuntu16 |
 | TF 1.5, 2.0 | custom-op-ubuntu16-cuda10.0 | custom-op-gpu-ubuntu16 |
 | TF <= 1.4 | custom-op-ubuntu14 | custom-op-gpu-ubuntu14 |