Add support for DefaultDict on jedi_typing.py.

[tarcisioe]

Fixes #1144.

[codecov-io]

Codecov Report

Merging #1145 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1145   +/-   ##
=======================================
  Coverage   92.78%   92.78%           
=======================================
  Files          57       57           
  Lines        6902     6902           
=======================================
  Hits         6404     6404           
  Misses        498      498

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 70c2fce...24f49a6. Read the comment docs.

[davidhalter]

Can you add a test for it as well. Thanks for the fast fix!

[tarcisioe]

I wasn't sure what to test, so I duplicated the tests that were done to typing.Dict. as well. I also didn't know how to support the instance variable default_factory that DefaultDicts have, because all other typing stubs only have methods and I didn't know how I could type a variable (no type annotations are used on the file, and it would be Python 3.6 only if I used variable annotations).

[davidhalter]

This is good enough. Dict in typing.py is pretty much the same as DefaultDict anyway, because there is no way to figure out if a key is present in a dict. Thanks for the tests!