SPEC: Fix documentation example for ABC Size

[a-leung]

The given code example has an ABC size of 6.4, but comments list the
calculation as:

Math.sqrt(11 + 55 + 2*2)

which results in: 5.48.

The correct calculation for the given the example are:

Math.sqrt(11 + 66 + 2*2) = 6.40

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Used the same coding conventions as the rest of the project.
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• All tests are passing.
• The new code doesn't generate RuboCop offenses.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Updated cop documentation with rake generate_cops_documentation (required only when you've added a new cop or changed the configuration/documentation of an existing cop).

[bbatsov]

Wow! So impressive you managed to spot this! Thanks! 👍

[a-leung]

no problem! I was doing some research on an article I wrote and found it.

thanks again for all your work on Rubocop!