Fix RuboCop 0.40 linter errors (#1722)

These errors are breaking the build, which seems to use RuboCop 0.40 [1]
despite the Gemfile.lock pinning rubocop to 0.38.

New lints that I am updating the code style to reflect:

- Style/EmptyCaseCondition: Do not use empty case condition, instead use
  an if expression.

- Style/MultilineArrayBraceLayout: Closing array brace must be on the
  same line as the last array element when opening brace is on the same
  line as the first array element.

- Style/MultilineHashBraceLayout: Closing hash brace must be on the same
  line as the last hash element when opening brace is on the same line
  as the first hash element.

- Style/MultilineMethodCallBraceLayout: Closing method call brace must
  be on the line after the last argument when opening brace is on a
  separate line from the first argument.

[1] https://github.com/bbatsov/rubocop/releases/tag/v0.40.0

test/adapter/json_api/collection_test.rb

@@ -58,9 +58,10 @@ module ActiveModelSerializers
 
         def test_limiting_fields
           actual = ActiveModelSerializers::SerializableResource.new(
-            [@first_post, @second_post], adapter: :json_api,
-                                         fields: { posts: %w(title comments blog author) })
-                                                               .serializable_hash
+            [@first_post, @second_post],
+            adapter: :json_api,
+            fields: { posts: %w(title comments blog author) }
+          ).serializable_hash
           expected = [
             {
               id: '1',