require date before activesupport/core_ext

Work around a TypeMismatchError with Ruby 2.0 and
ActiveSupport 4.0.0 when only requiring core_ext.
Merge pull request #152 from jkraemer/fix_type_mismatch

work around for TypeMismatch error
modify to "Only supports Ruby 1.9 and later"
indent multi line
delete new-line before tweet info
add rake