Drop support for Ruby 1.8.7 and 1.9.2
Revert "Restore Ruby 1.8.7 compatibility"

This reverts commit e29af783bbc4b162f067342c6da0506fe3e84e0e.
Revert "Fix specs on Ruby 1.8.7"

This reverts commit 353adb32fb227a8f8b5b643e319c578de026457d.