Update rspec.

Note that this exposed an rspec-mocks bug that I plan to tackle soon:

https://github.com/rspec/rspec-mocks/issues/217
Resolve constant name starting at Object rather than Kernel.

Kernel works fine when the constant is defined, but when it
is undefined, it leads to a confusing error:

`undefined constant Kernel::MyJob`

...rather than:

`undefined constant MyJob`