Remove deprecated rspec usage of `should_not raise_error`
Change Proc.should_not to expect{}.to_not
use rspec `stub` instead of `stub!`
Remove a few duplicate expectations

We already expect this code to raise a specific error Class (OEmbed::UnknownResponse). Therefore we know that this specific code will not be raising these other error classes.
Merge pull request #3 from metavida/update_rspec_syntax

Update rspec syntax