Fix mistake in RSpec/PredicateMatcher doc

Author: pirj

lib/rubocop/cop/rspec/predicate_matcher.rb

@@ -277,12 +277,12 @@ def replacement_matcher(node)
       #   expect(foo).to be_something
       #
       #   # also good - It checks "true" strictly.
-      #   expect(foo).to be(true)
+      #   expect(foo.something?).to be(true)
       #
       # @example Strict: false, EnforcedStyle: inflected
       #   # bad
       #   expect(foo.something?).to be_truthy
-      #   expect(foo).to be(true)
+      #   expect(foo.something?).to be(true)
       #
       #   # good
       #   expect(foo).to be_something

manual/cops_rspec.md

@@ -2452,14 +2452,14 @@ expect(foo.something?).to be_truthy
 expect(foo).to be_something
 
 # also good - It checks "true" strictly.
-expect(foo).to be(true)
+expect(foo.something?).to be(true)
 ```
 #### Strict: false, EnforcedStyle: inflected
 
 ```ruby
 # bad
 expect(foo.something?).to be_truthy
-expect(foo).to be(true)
+expect(foo.something?).to be(true)
 
 # good
 expect(foo).to be_something