add ActiveSupport::Base64 check.

ActiveSupport::Base64 was deleted in ActiveSupport 4.0. https://github.com/rails/rails/commit/44df252382cc2301364495ff65563d23bcc1b070
change to ActiveSupport::JSON.parse_error to catch JSON parse error.

https://github.com/rails/rails/commit/053a0f6ac48d35fd39d385df5d810078e92c521e
Merge pull request #6 from miyucy/better-compatibility

Better compatibility