v2.15.0

Changes:

• Added Ruby 3.0 to supported versions
• Ruby 2.5 is now a required minimum version (we dropped official support for Ruby versions older than 2.5 about 8 months ago)
• Added skip_canonical_links_on_noindex configuration variable that allows to disable canonical links of the pages that are excluded from indexing (214)
• Added support for itemprop in _ tag for custom tags (203)

Bugfixes:

• Fixed error "can't modify frozen String" in strip_tags.
• Fixed Ruby warning about an instance variable that is not initialized.