Fix Ruby's warnings about mismatched indentation

[parndt]

This is to fix these warnings:

lib/stripe/api_operations/nested_resource.rb:55: warning: mismatched indentations at 'end' with 'do' at 48
lib/stripe/api_operations/nested_resource.rb:83: warning: mismatched indentations at 'end' with 'do' at 59
lib/stripe/api_operations/nested_resource.rb:93: warning: mismatched indentations at 'end' with 'do' at 86
lib/stripe/api_operations/nested_resource.rb:103: warning: mismatched indentations at 'end' with 'do' at 96
lib/stripe/api_operations/nested_resource.rb:113: warning: mismatched indentations at 'end' with 'do' at 106

Similar work was done in #852

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}