azure-mgmt-rdbms==8.1.0b3 breaks linter

Using the latest version of azdev (0.1.32), we see the following error when running `azdev linter `

```
Initializing linter with command table and help files...
ERROR: The operation 'azure.mgmt.rdbms.postgresql.operations#ReplicasOperations.list_by_server' is invalid.
Traceback (most recent call last):
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/azure/cli/core/__init__.py", line 852, in get_op_handler
op = getattr(op, part)
AttributeError: module 'azure.mgmt.rdbms.postgresql.operations' has no attribute 'ReplicasOperations'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/knack/cli.py", line 231, in invoke
cmd_result = self.invocation.execute(args)
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/knack/invocation.py", line 223, in execute
cmd_result = parsed_args.func(params)
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/knack/commands.py", line 146, in __call__
return self.handler(*args, **kwargs)
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/knack/commands.py", line 253, in _command_handler
result = op(client, **command_args) if client else op(**command_args)
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/azdev/operations/linter/__init__.py", line 118, in run_linter
create_invoker_and_load_cmds_and_args(az_cli)
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/azure/cli/core/file_util.py", line 74, in create_invoker_and_load_cmds_and_args
invoker.commands_loader.load_arguments()
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/azure/cli/core/__init__.py", line 496, in load_arguments
cmd.load_arguments() # this loads the arguments via reflection
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/azure/cli/core/commands/__init__.py", line 313, in load_arguments
super(AzCliCommand, self).load_arguments()
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/knack/commands.py", line 104, in load_arguments
cmd_args = self.arguments_loader()
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/azure/cli/core/__init__.py", line 810, in default_arguments_loader
op = handler or self.get_op_handler(operation, operation_group=kwargs.get('operation_group'))
File "/var/lib/jenkins/workspace/verification-pipeline-server-unittests/az-cli/.azdev/azdev-env/lib64/python3.6/site-packages/azure/cli/core/__init__.py", line 857, in get_op_handler
raise ValueError("The operation '{}' is invalid.".format(operation))
ValueError: The operation 'azure.mgmt.rdbms.postgresql.operations#ReplicasOperations.list_by_server' is invalid.
```

Switching back to azure-mgmt-rdbms==8.1.0b2 appears to address the problem.