Fix gemspec

[cthulhu666]

WARNING:  licenses is empty, but is recommended.  Use a license identifier from
http://spdx.org/licenses or 'Nonstandard' for a nonstandard license.
WARNING:  no homepage specified
WARNING:  description and summary are identical
WARNING:  open-ended dependency on activemodel (> 4.2) is not recommended
  if activemodel is semantically versioned, use:
    add_runtime_dependency 'activemodel', '~> 4.2', '> 4.2'
WARNING:  open-ended dependency on actionpack (> 4.2) is not recommended
  if actionpack is semantically versioned, use:
    add_runtime_dependency 'actionpack', '~> 4.2', '> 4.2'
WARNING:  open-ended dependency on appraisal (>= 0, development) is not recommended
  if appraisal is semantically versioned, use:
    add_development_dependency 'appraisal', '~> 0'
WARNING:  See http://guides.rubygems.org/specification-reference/ for help
  Successfully built RubyGem
  Name: easy_table
  Version: 0.0.9
  File: easy_table-0.0.9.gem