Bump RuboCop Performance to 1.10

This PR bumps RuboCop Performance to 1.10 and suppresses the new
`Performance/RedundantSplitRegexpArgument` cop's offenses.

```console
% bundle exec rubocop
(snip)

Offenses:

lib/rubocop/cop/mixin/preferred_delimiters.rb:18:42: C: [Corrected]
Performance/RedundantSplitRegexpArgument: Use string as argument instead
of regexp.
        preferred_delimiters[type].split(//)
                                         ^^
lib/rubocop/cop/mixin/preferred_delimiters.rb:18:42: C: [Corrected]
Style/StringLiterals: Prefer single-quoted strings when you don't need
string interpolation or special symbols.
        preferred_delimiters[type].split("")
                                         ^^
lib/rubocop/cop/style/command_literal.rb:168:58: C: [Corrected]
Performance/RedundantSplitRegexpArgument: Use string as argument instead
of regexp.
          (command_delimiter || default_delimiter).split(//)
                                                         ^^
lib/rubocop/cop/style/command_literal.rb:168:58: C: [Corrected]
Style/StringLiterals: Prefer single-quoted strings when you don't need
string interpolation or special symbols.
          (command_delimiter || default_delimiter).split("")
                                                         ^^
lib/rubocop/cop/style/regexp_literal.rb:153:49: C: [Corrected]
Performance/RedundantSplitRegexpArgument: Use string as argument instead
of regexp.
            ['PreferredDelimiters']['%r'].split(//)
                                                ^^
lib/rubocop/cop/style/regexp_literal.rb:153:49: C: [Corrected]
Style/StringLiterals: Prefer single-quoted strings when you don't need
string interpolation or special symbols.
            ['PreferredDelimiters']['%r'].split("")
                                                ^^
spec/support/alignment_examples.rb:11:26: C: [Corrected]
Performance/RedundantSplitRegexpArgument: Use string as argument instead
of regexp.
  annotated_source.split(/\n\n/).each do |chunk|
                         ^^^^^^

1265 files inspected, 7 offenses detected, 7 offenses corrected
```

Gemfile

@@ -14,7 +14,7 @@ else
 end
 gem 'rake', '~> 13.0'
 gem 'rspec', '~> 3.7'
-gem 'rubocop-performance', '~> 1.9.0'
+gem 'rubocop-performance', '~> 1.10.0'
 gem 'rubocop-rspec', '~> 2.2.0'
 # Workaround for cc-test-reporter with SimpleCov 0.18.
 # Stop upgrading SimpleCov until the following issue will be resolved.

lib/rubocop/cop/mixin/preferred_delimiters.rb

@@ -15,7 +15,7 @@ def initialize(type, config, preferred_delimiters)
       end
 
       def delimiters
-        preferred_delimiters[type].split(//)
+        preferred_delimiters[type].split('')
       end
 
       private

lib/rubocop/cop/style/command_literal.rb

@@ -165,7 +165,7 @@ def backtick_literal?(node)
         end
 
         def preferred_delimiter
-          (command_delimiter || default_delimiter).split(//)
+          (command_delimiter || default_delimiter).split('')
         end
 
         def command_delimiter

lib/rubocop/cop/style/regexp_literal.rb

@@ -150,7 +150,7 @@ def slash_literal?(node)
 
         def preferred_delimiters
           config.for_cop('Style/PercentLiteralDelimiters') \
-            ['PreferredDelimiters']['%r'].split(//)
+            ['PreferredDelimiters']['%r'].split('')
         end
 
         def correct_delimiters(node, corrector)

spec/support/alignment_examples.rb

@@ -8,7 +8,7 @@
                              else
                                { 'Enabled' => false }
                              end
-  annotated_source.split(/\n\n/).each do |chunk|
+  annotated_source.split("\n\n").each do |chunk|
     chunk << "\n" unless chunk.end_with?("\n")
     source = chunk.lines.reject { |line| /^ *\^/.match?(line) }.join
     name = source.gsub(/\n(?=[a-z ])/, ' <newline> ').gsub(/\s+/, ' ')