Fix Ruby's warnings about mismatched indentation

[parndt]

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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

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[helenye-stripe]

Sorry about the delay here! Fixed in https://github.com/stripe/stripe-ruby/pull/1584