Completed "Sorting and limiting posts", Section 10.

Calling Blog::Blog#entries now returns the last 10 entries in reverse chronological order.

RSpec: 78 examples, 0 failures
Script: 0 tests: 0 failures, 0 errors, 0 pending, 0 omitted
RuboCop: 28 files inspected, no offenses detected
RuboCop global overrides in `.rubocop.yml`: 4
RuboCop local overrides in source and own specs: 1