Fixed issue with ```Traceback (most recent call last):   File "/usr/local/bin/azure-shell", line 11, in <module>     sys.exit(main())   File "/usr/local/lib/python3.6/site-packages/azureshell/__init__.py", line 46, in main     if azure_cli_version < AZURE_SHELL_MINIMUM_AZURE_CLI_VERSION: TypeError: '<' not supported between instances of 'NoneType' and 'str'```
Fixed issue with
```Traceback (most recent call last):
  File "/usr/local/bin/azure-shell", line 11, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.6/site-packages/azureshell/__init__.py", line 46, in main
    if azure_cli_version < AZURE_SHELL_MINIMUM_AZURE_CLI_VERSION:
TypeError: '<' not supported between instances of 'NoneType' and 'str'```

yokawasa/azure-shell,yokawasa/azure-shell