downloads: upgrade CPython 3.8 to 3.8.3

It was released a few days ago. It contains at least 1 fix related
to multiple Python interpreters in a single process that will benefit
PyOxidizer.

Author: indygreg

pythonbuild/downloads.py

@@ -62,10 +62,10 @@
         "python_tag": "cp37",
     },
     "cpython-3.8": {
-        "url": "https://www.python.org/ftp/python/3.8.2/Python-3.8.2.tar.xz",
-        "size": 17869888,
-        "sha256": "2646e7dc233362f59714c6193017bb2d6f7b38d6ab4a0cb5fbac5c36c4d845df",
-        "version": "3.8.2",
+        "url": "https://www.python.org/ftp/python/3.8.3/Python-3.8.3.tar.xz",
+        "size": 17912964,
+        "sha256": "dfab5ec723c218082fe3d5d7ae17ecbdebffa9a1aea4d64aa3a2ecdd2e795864",
+        "version": "3.8.3",
         "licenses": ["Python-2.0", "CNRI-Python"],
         "license_file": "LICENSE.cpython.txt",
         "python_tag": "cp38",