emacsPackages.melpaPackages: Ignore Git SSL certs

There are a number of derivations failing because we are lacking the
required certs.

fetchurl is already ignoring certs so I figured we'd do the same.

pkgs/applications/editors/emacs-modes/libgenerated.nix

@@ -25,10 +25,12 @@ let
         }
       ) {};
       git = self.callPackage ({ fetchgit }:
-        fetchgit {
+        (fetchgit {
           rev = commit;
           inherit sha256 url;
-        }
+        }).overrideAttrs(_: {
+          GIT_SSL_NO_VERIFY = true;
+        })
       ) {};
       bitbucket = self.callPackage ({ fetchhg }:
         fetchhg {