Log Message:
Update drupal8 to 8.7.8

Core versioning support in *.info.yml files since 8.7.7

   Drupal 8.7.7 introduces a new core_version_requirement key to
   *.info.yml files, allowing contributed modules to specify specific
   versions for Drupal core compatiblity, as well as to indicate that they
   are compatible with both Drupal 8 and the forthcoming Drupal 9 release.
   See the change record for more details.

Dependency updates

     * Several JavaScript dependencies have been updated to resolve
       publicly disclosed security issues:
          + nightwatch has been updated to version 1.2.1
          + chromedriver has been updated to version 75.1.0
          + stylelint-no-browser-hacks has been updated to 1.2.1
     * Due to a compatibility issue between zend-diactoros 1.8.5 and
       psr-http-message-bridge versions prior to 1.1.2, Drupal core's
       composer.json has increased the minimum requirement for
       psr-http-message-bridge from 1.0 to 1.1.2. This should not affect
       sites using the tarball packaged by Drupal.org (which already
       supplied version 1.1.2 of the component in Drupal 8.7.7), but may
       lead to a dependency update for certain sites maintained with
       Composer.

Full release notes available at:
https://www.drupal.org/project/drupal/releases/8.7.8