Fix release instructions

[ci skip]
:cut: whitespace
Merge branch 'master' of github.com:rails/rails

* 'master' of github.com:rails/rails:
  Fix release instructions
  Raise an error when AS::JSON.decode is called with options
  Moved all JSON core extensions into core_ext/object/json
rename AppPreparer

AppPreparer doesn't actually prepare applications, it scrubs ARGV.
Let's also get the class under test while we're at it
prepare! should return argv
stop mutating ARGV
forgot the test, oops!
test some of the rc specification
remove useless assertions
add a test for the rc commandline option
adding a test for the current behavior
change the test to make argv a little more realistic