Fix example code in README.md

To upload file, `curl` requires `@` at the beginning of file path.
Merge pull request #532 from tricknotes/fix-example-in-readme

Fix example code in README.md
Helpers are now available to auth middleware, executing in the context of the endpoint.
Fix rescue_from example
Merge pull request #536 from styx/patch-2

Fix rescue_from example
added failing spec: default values for grouped parameters
Fix default values for grouped params
Merge pull request #538 from dm1try/fix_default_values_for_group_params

Fix default values for group params
Pull grape-active_model_serializers into new section in readme
Merge pull request #539 from jrhe/master

Mention grape-active_model_serializers in readme
Lock RSpec version, failing with rspec-expectations 3.x beta.
Added Ruby 2.1 support.
Fix for https://github.com/travis-ci/travis-ci/issues/1800.
Rescue subclasses in error middleware.
Fix typo in rescue_from unit test (Communication --> Communications).
Merge pull request #546 from xevix/fix_rescue_from_unit_test

Fix typo in rescue_from unit test (Communication --> Communications).
Rename children --> subclasses to match the name used in the code.
Remove unnecessary test case.
Address #543 - raise proper validation errors on array/hash types

 * Also adds a :type option to group/requires/optional with block,
   which can either be Array or Hash. It defaults to Array.

 * Fixes (2) and (3) as mentioned in #543

 * There is a quirk around query parameters: an empty array should
   pass validation if the array itself is required, but with how
   query parameters work, it doesn't. It does work fine with body
   parameters using JSON or similar, which do have a concept of an
   empty array.
README.md and UPGRADE.md update for #543, #545