textproc/rubygem-nokogiri: Update to 1.13.10

- Remove LIB_DEPENDS:
  - libxml2 is already in USE_GNOME
  - libgcrypt and libgpg-error are indirect dependencies (via libxslt)
- Clean up:
  - Remove rubygem-pkg-config from RUN_DEPENDS by moving it to BUILD_DEPENDS
  - Remove USES=pkgconfig
  - Remove STRIP_CMD from post-install: since it is done by USES=gem
- Update version requirement of BUILD_DEPENDS

Changes:	https://github.com/sparklemotion/nokogiri/releases