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/linked_test.rb

@@ -341,9 +341,10 @@ module ActiveModelSerializers
 
         def test_no_duplicates_collection
           hash = ActiveModelSerializers::SerializableResource.new(
-            [@post1, @post2], adapter: :json_api,
-                              include: '*.*')
-                                                             .serializable_hash
+            [@post1, @post2],
+            adapter: :json_api,
+            include: '*.*'
+          ).serializable_hash
           expected = [
             {
               type: 'authors', id: '1',
@@ -364,7 +365,8 @@ module ActiveModelSerializers
           hash = ActiveModelSerializers::SerializableResource.new(
             @nestedpost1,
             adapter: :json_api,
-            include: '*').serializable_hash
+            include: '*'
+          ).serializable_hash
           expected = [
             type: 'nested-posts', id: '2',
             relationships: {
@@ -383,7 +385,8 @@ module ActiveModelSerializers
           hash = ActiveModelSerializers::SerializableResource.new(
             [@nestedpost1, @nestedpost2],
             adapter: :json_api,
-            include: '*').serializable_hash
+            include: '*'
+          ).serializable_hash
           assert_nil(hash[:included])
         end
       end