Fix invalid response and rename ListPlanAccountsForAccount (fixes #1270)

[sethaustinx]

To simplify review and address specific requests from #1270 (comment) I've made separate commits.

Also wording doesn't seem to match GitHub docs anymore.

If that's ok @gmlewis, I'd like to rename:

• GetPlanAccountForAccount to GetSubscriptionPlanForAccount https://octokit.github.io/rest.js/v18#apps-get-subscription-plan-for-account
• MarketplacePlanAccount to MarketplaceSubscriptionPlan

What do you think?

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[sethaustinx]

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[codecov]

Codecov Report

Merging #1827 (5bfa385) into master (94eb482) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1827      +/-   ##
==========================================
+ Coverage   97.56%   97.59%   +0.02%     
==========================================
  Files         104      104              
  Lines        6602     6599       -3     
==========================================
- Hits         6441     6440       -1     
+ Misses         87       86       -1     
+ Partials       74       73       -1     

Impacted Files	Coverage Δ
github/apps_marketplace.go	88.23% <100.00%> (+3.05%)	⬆️

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[gmlewis]

If that's ok @gmlewis, I'd like to rename:

• GetPlanAccountForAccount to GetSubscriptionPlanForAccount https://octokit.github.io/rest.js/v18#apps-get-subscription-plan-for-account
• MarketplacePlanAccount to MarketplaceSubscriptionPlan

What do you think?

Yes, those seem like reasonable changes (since we are already breaking the API).
Thank you, @sethaustinx . I'll take a look at your PR.

[gmlewis]

Thank you, @sethaustinx !
LGTM.

Awaiting second LGTM before merging.

[wesleimp]

💙

[gmlewis]

Thank you, @wesleimp !
Merging.

[sethaustinx]

Awesome 🧡