fix($injector): ensure $get method invoked with provider context

0d3b69a5f27b41745b504c7ffd8d72653bac1f85 broke this by calling $get with an undefined
context, which in strict mode would be undefined. This fixes this by ensuring that the
provider is used as the context, as it was originally.

Closes #9511
Closes #9512
chore(injectorSpec.js): make jshint happy

...oops ._.