Enable cop for pending rubocop-performance

```
❯ bundle exec rubocop
Inspecting 42 files
.......................................C..

Offenses:

spec/spec_helper.rb:17:9: C: Performance/MethodObjectAsBlock: Use block explicitly instead of block-passing a method object.
  .each(&method(:require))
        ^^^^^^^^^^^^^^^^^

42 files inspected, 1 offense detected
```

.rubocop.yml

@@ -135,6 +135,43 @@ Style/RedundantStringEscape:
 Style/ReturnNilInPredicateMethodDefinition:
   Enabled: true
 
+# Enable pending rubocop-performance cops.
+
+Performance/AncestorsInclude:
+  Enabled: true
+Performance/BlockGivenWithExplicitBlock:
+  Enabled: true
+Performance/CollectionLiteralInLoop:
+  Enabled: true
+Performance/ConstantRegexp:
+  Enabled: true
+Performance/MapCompact:
+  Enabled: true
+Performance/MapMethodChain:
+  Enabled: true
+Performance/MethodObjectAsBlock:
+  Enabled: true
+Performance/RedundantEqualityComparisonBlock:
+  Enabled: true
+Performance/RedundantSortBlock:
+  Enabled: true
+Performance/RedundantSplitRegexpArgument:
+  Enabled: true
+Performance/RedundantStringChars:
+  Enabled: true
+Performance/ReverseFirst:
+  Enabled: true
+Performance/SortReverse:
+  Enabled: true
+Performance/Squeeze:
+  Enabled: true
+Performance/StringIdentifierArgument:
+  Enabled: true
+Performance/StringInclude:
+  Enabled: true
+Performance/Sum:
+  Enabled: true
+
 # Enable pending rubocop-rspec cops.
 
 RSpec/BeEmpty:

spec/spec_helper.rb

@@ -14,7 +14,7 @@ module SpecHelper
 Dir
   .glob(File.expand_path(spec_helper_glob, __dir__))
   .sort
-  .each(&method(:require))
+  .each { |file| require file }
 
 RSpec.configure do |config|
   # Set metadata so smoke tests are run on all cop specs