Bump zlib from 1.2.13 -> 1.3.1 (#357)

Author: zanieb

pythonbuild/downloads.py

@@ -404,10 +404,10 @@
         "license_public_domain": True,
     },
     "zlib": {
-        "url": "https://github.com/madler/zlib/releases/download/v1.2.13/zlib-1.2.13.tar.gz",
-        "size": 1497445,
-        "sha256": "b3a24de97a8fdbc835b9833169501030b8977031bcb54b3b3ac13740f846ab30",
-        "version": "1.2.13",
+        "url": "https://github.com/madler/zlib/releases/download/v1.3.1/zlib-1.3.1.tar.gz",
+        "size": 1512791,
+        "sha256": "9a93b2b7dfdac77ceba5a558a580e74667dd6fede4585b91eefb60f03b72df23",
+        "version": "1.3.1",
         "library_names": ["z"],
         "licenses": ["Zlib"],
         "license_file": "LICENSE.zlib.txt",