Supress Style/RedundantStringEscape's offenses

This commit supresses the following `Style/RedundantStringEscape`'s offenses.

```console
% bundle exec rake
(snip)

Offenses:

spec/rubocop/cop/performance/fixed_size_spec.rb:50:29: C: [Corrected] Style/RedundantStringEscape:
Redundant escape of % inside string literal.
expect_no_offenses("\%Q(\#{foo}).#{method}")
                    ^^
spec/rubocop/cop/performance/fixed_size_spec.rb:54:29: C: [Corrected] Style/RedundantStringEscape:
Redundant escape of % inside string literal.
expect_no_offenses("\%(\#{foo}).#{method}")
                    ^^
spec/rubocop/cop/performance/redundant_split_regexp_argument_spec.rb:66:34: C: [Corrected] Style/RedundantStringEscape:
Redundant escape of % inside string literal.
"foo\\\\\\.bar".split("\\\\\.")
                           ^^
spec/rubocop/cop/performance/string_replacement_spec.rb:47:27: C: [Corrected] Style/RedundantStringEscape:
Redundant escape of % inside string literal.
'abc'.#{method}(\"\#{foo}\", '1')
                ^^
spec/rubocop/cop/performance/string_replacement_spec.rb:47:36: C: [Corrected] Style/RedundantStringEscape:
Redundant escape of % inside string literal.
'abc'.#{method}(\"\#{foo}\", '1')
                         ^^
spec/rubocop/cop/performance/string_replacement_spec.rb:54:32: C: [Corrected] Style/RedundantStringEscape:
Redundant escape of % inside string literal.
'abc'.#{method}('a', \"\#{foo}\")
                     ^^
spec/rubocop/cop/performance/string_replacement_spec.rb:54:41: C: [Corrected] Style/RedundantStringEscape:
Redundant escape of % inside string literal.
'abc'.#{method}('a', \"\#{foo}\")
                              ^^

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

spec/rubocop/cop/performance/fixed_size_spec.rb

@@ -47,11 +47,11 @@
       end
 
       it "accepts calling #{method} on a %Q string that contains interpolation" do
-        expect_no_offenses("\%Q(\#{foo}).#{method}")
+        expect_no_offenses("%Q(\#{foo}).#{method}")
       end
 
       it "accepts calling #{method} on a % string that contains interpolation" do
-        expect_no_offenses("\%(\#{foo}).#{method}")
+        expect_no_offenses("%(\#{foo}).#{method}")
       end
 
       it "accepts calling #{method} on a single quoted string that is assigned to a constant" do

spec/rubocop/cop/performance/redundant_split_regexp_argument_spec.rb

@@ -63,7 +63,7 @@
     RUBY
 
     expect_correction(<<~RUBY)
-      "foo\\\\\\.bar".split("\\\\\.")
+      "foo\\\\\\.bar".split("\\\\.")
     RUBY
   end
 

spec/rubocop/cop/performance/string_replacement_spec.rb

@@ -44,14 +44,14 @@
       it 'accepts a pattern with string interpolation' do
         expect_no_offenses(<<~RUBY)
           foo = 'a'
-          'abc'.#{method}(\"\#{foo}\", '1')
+          'abc'.#{method}("\#{foo}", '1')
         RUBY
       end
 
       it 'accepts a replacement with string interpolation' do
         expect_no_offenses(<<~RUBY)
           foo = '1'
-          'abc'.#{method}('a', \"\#{foo}\")
+          'abc'.#{method}('a', "\#{foo}")
         RUBY
       end