Enable Enabled parameter

When the project configured as:
```yaml
# .rubocop.yml

require:
  - rubocop-rspec

AllCops:
  DisabledByDefault: true

RSpec:
  Enabled: true
```

an annoying warning pops up:
```
Warning: RSpec does not support Enabled parameter.

Supported parameters are:

  - Include
  - Language
```

This is not the case with e.g. `rubocop-rails`. Apparently, this is due
to our RSpec DSL configuration, as `rubocop-rails` doesn't have any
`Rails:` YAML configuration in their `config/default.yml`.

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 * Fix `HooksBeforeExamples`, `LeadingSubject`, `LetBeforeExamples` and `ScatteredLet` autocorrection to take into account inline comments and comments immediately before the moved node. ([@Darhazer][])
 * Improve rubocop-rspec performance. ([@Darhazer][])
+* Include `Enabled: true` to prevent a mismatched configuration parameter warning when `RSpec` cops are explicitly enabled in the user configuration. ([@pirj][])
 
 ## 2.1.0 (2020-12-17)
 

config/default.yml

@@ -1,5 +1,6 @@
 ---
 RSpec:
+  Enabled: true
   Include:
     - "**/*_spec.rb"
     - "**/spec/**/*"