Deleting a global option persists for all instances

[mercyaj]

Possibly related to #135

Describe the bug
When deleting/overwriting a global option in one instance of useFetch, the global options are then permanently modified across all instances.

Following the example in the README:

 // let's say for this request, you don't want the `Accept` header at all
  const { loading, error, data: todos } = useFetch(globalOptions => {
    delete globalOptions.headers.Accept
    return {
      data: [],
      ...globalOptions
    }
  }, []) // onMount

This line:
delete globalOptions.headers.Accept

Will delete the Accept header for all useFetch instances across an app.

⚠️ Make a Codesandbox ⚠️
https://codesandbox.io/embed/goofy-bird-yhon5?fontsize=14&hidenavigation=1&theme=dark

To Reproduce
Steps to reproduce the behavior:

1. Go to Login page
2. Click on "Login" button
3. Open the console - the Todo useFetch options do not have the interceptors.request property that is defined in the global options passed to the Provider.

Expected behavior
I would expect that modifying the global options in an instance of useFetch would create a local copy and would not affect the global options in any other instances.

[iamthesiz]

Thank you! Will get to this asap. If you get to it before me/would like to contribute, here's how.

[iamthesiz]

This should be fixed as of v1.0.8. If the issue persists, let me know. I'll reopen the issue.

[mercyaj]

@alex-cory unfortunately I'm still experiencing issues with this in v1.0.8. I've updated the Codesandbox to show the new issue. I believe the problem lies here. The fix merged above works for headers but not interceptors.

[iamthesiz]

Apologies for missing that. Will get it merged today.

[iamthesiz]

should be fixed in v1.0.10