fix: 🐛 check for rlogin is None

[onuralpszr]

Description

I notice that if I type random string or invalid key it was creating folder and AttributeError occured. I added check in the begin and if response is NONE, I added ValueError for prevent unneeded process and stop the login

List any dependencies that are required for this change.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How has this change been tested, please provide a testcase or example of how you tested the change?

Current Error

>>> import roboflow
>>> roboflow.login()
visit https://app.roboflow.com/auth-cli to get your authentication token.
Paste the authentication token here:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/onuralp/roboflow/roboflow-python/roboflow/__init__.py", line 126, in login
    default_workspace_id = list(r_login["workspaces"].keys())[0]
AttributeError: 'NoneType' object has no attribute 'keys'

Fixed Version (Controlled Error)

>>> import roboflow
>>> roboflow.login()
visit https://app.roboflow.com/auth-cli to get your authentication token.
Paste the authentication token here:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/onuralp/roboflow/roboflow-python/roboflow/__init__.py", line 118, in login
    raise ValueError("Invalid API key. "
ValueError: Invalid API key. Please check your API key and try again.

[capjamesg]

I wonder if we should have an AuthenticationError class one day that represents different errors that can occur. That's just me brainstorming though! This looks good to me.

[capjamesg]

@onuralpszr Can you run your PR through black? The PR is failing the black test in our CI.

[capjamesg]

Thank you for fixing the linting issues! Will merge!

[onuralpszr]

@capjamesg yay thank you ! :)