gettext_lazy should return a Promise object

[PIG208]

Bug report

The type annotation added in #126 is incorrect.

What's wrong

from django.utils.translation import gettext_lazy, ngettext_lazy, pgettext_lazy, ugettext_lazy
from django.utils.functional import Promise

a = gettext_lazy("Help")
b = ugettext_lazy("Help")
c = pgettext_lazy("Help")
d = ngettext_lazy("help", "helps")
e = ugettext_lazy("Help")

assert isinstance(a, Promise)
assert isinstance(b, Promise)
assert isinstance(c, Promise)
assert isinstance(d, Promise)
assert isinstance(e, Promise)

How is that should be

For all lazy functions above, django-stubs consider the return type to be str, which is actually incorrect. All of them are in fact instances of django.utils.functional.Promise

[sobolevn]

@PIG208 PRs are welcome!

[PIG208]

@sobolevn Just created a PR for this :)