Disable RSpec/NoExpectationExample

As discussed below issue, there are many cases of false positives,
and some exsamples are intentionally no expectation.

https://togithub.com/rubocop/rubocop-rspec/issues/1385

```
spec/selector_spec.rb:120:27: C: RSpec/Capybara/SpecificMatcher: Prefer have_no_field over have_no_css.
        expect(string).to have_no_css('input[type="hidden"]')
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

.rubocop.yml

@@ -166,6 +166,9 @@ RSpec/ContextWording:
 RSpec/NestedGroups:
   Enabled: false
 
+RSpec/NoExpectationExample:
+  Enabled: false
+
 RSpec/DescribeClass:
   Enabled: false