python37Packages.cryptography: 2.7 -> 2.8

Changelog:
https://cryptography.io/en/latest/changelog/#v2-8

Important changes:
- Deprecated support for OpenSSL 1.0.1. Support will be removed in
  cryptography 2.9.
- cryptography no longer depends on asn1crypto.
- Added support for Python 3.8.

pkgs/development/python-modules/cryptography/vectors.nix

@@ -7,7 +7,7 @@ buildPythonPackage rec {
 
   src = fetchPypi {
     inherit pname version;
-    sha256 = "1g38zw90510azyfrj6mxbslx2gp9yrnv5dac0w2819k9ssdznbgi";
+    sha256 = "05pi3shqz0fgvy0d5yazza67bbnam8fkrx2ayrrclgkaqms23lvc";
   };
 
   # No tests included