Fix EknImagePreviewer:aspect type
Fix EknImagePreviewer:aspect type

The parameter doesn't need to be a float, it can be a regular double;
the arguments were incorrect, which newer GJS doesn't like; and I fixed
a typo in the documentation.

[endlessm/eos-sdk#3069]

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib