azure-cli: aks-preview extension breaks most az aks commands

Describe the bug aks-preview extension broke az aks get-credentials. This was working perfectly prior to Nov 13 2019.

To Reproduce

bash-4.2# az --version
azure-cli                         2.0.75

command-modules-nspkg              2.0.3
core                              2.0.75
nspkg                              3.0.4
telemetry                          1.0.4

Python location '/usr/bin/python'
Extensions directory '/home/jenkins/.azure/cliextensions'

Python (Linux) 2.7.5 (default, Jun 11 2019, 14:33:56)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-39)]

Legal docs and information: aka.ms/AzureCliLegal

bash-4.2# ls -l /home/jenkins/.azure/cliextensions/aks-preview/azext_aks_preview/custom.py
ls: cannot access /home/jenkins/.azure/cliextensions/aks-preview/azext_aks_preview/custom.py: No such file or directory

bash-4.2# az aks get-credentials -n aks-testing -g rsg-testing -a -f admin.kubeconfig
Merged "aks-testing" as current context in admin.kubeconfig

bash-4.2# az extension add --name aks-preview

bash-4.2# ls -l /home/jenkins/.azure/cliextensions/aks-preview/azext_aks_preview/custom.py
-rw-r--r--. 1 root root 107080 Nov 13 07:17 /home/jenkins/.azure/cliextensions/aks-preview/azext_aks_preview/custom.py

bash-4.2# az aks get-credentials -n aks-testing -g rsg-testing -a -f admin.kubeconfig
The command failed with an unexpected error. Here is the traceback:

invalid syntax (custom.py, line 1155)
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/knack/cli.py", line 206, in invoke
    cmd_result = self.invocation.execute(args)
  File "/usr/lib/python2.7/site-packages/azure/cli/core/commands/__init__.py", line 523, in execute
    self.commands_loader.load_arguments(command)
  File "/usr/lib/python2.7/site-packages/azure/cli/core/__init__.py", line 291, in load_arguments
    self.command_table[command].load_arguments()  # this loads the arguments via reflection
  File "/usr/lib/python2.7/site-packages/azure/cli/core/commands/__init__.py", line 291, in load_arguments
    super(AzCliCommand, self).load_arguments()
  File "/usr/lib/python2.7/site-packages/knack/commands.py", line 97, in load_arguments
    cmd_args = self.arguments_loader()
  File "/usr/lib/python2.7/site-packages/azure/cli/core/__init__.py", line 488, in default_arguments_loader
    op = handler or self.get_op_handler(operation, operation_group=kwargs.get('operation_group'))
  File "/usr/lib/python2.7/site-packages/azure/cli/core/__init__.py", line 528, in get_op_handler
    op = import_module(mod_to_import)
  File "/usr/lib64/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
  File "/home/jenkins/.azure/cliextensions/aks-preview/azext_aks_preview/custom.py", line 1155
    f'save them to the storage account {colorama.Style.BRIGHT}{colorama.Fore.GREEN}{storage_account_name}{colorama.Style.RESET_ALL} as '
    ^
SyntaxError: invalid syntax

To open an issue, please run: 'az feedback'

Expected behavior az aks get-credentials will not fail

Environment summary install method is via pip: pip install --no-cache-dir --upgrade azure-cli running on a docker image with base openshift3/jenkins-slave-base-rhel7 tested in bash shell

Additional context This was working perfectly prior to Nov 13 2019.