Fix example description in QuickSpec.h

[muukii]

QuickSpec.spec() is instance method.

[phatblat]

True, the spec method is not a class method. However, that example is Swift in an Objective-C header. Would you mind changing the example to Objective-C?

[muukii]

@phatblat
Sure.
But, original example was written by Swift.
Still do you change it to Objective-C?

[phatblat]

Never mind. This example shows up in the docs for both objc and swift.

[muukii]

Thank you!