Fix typo. "client.client.get_merchant_account_status"

[kzkick2nd]

Description of changes:

I found a typo
response = client.client.get_merchant_account_status
in README.

I corrected the typo like this.
response = client.get_merchant_account_status

thank you.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[aiperon]

@kzkick2nd
First of all, I'm not a maintainer of this library. In order to see this library maintainable I want to help maintainers to clear opened PR list at first.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

What do you expect maintainer should do after reading that or accepting your PR? For me, it's confusing to see this comment in contribution.