octoprint: fix held back jinja2 dependency

Octoprint holds back python jinja2 package due to breaking changes.
nixpkgs' jinja2 recently changed to running tests, but the octoprint
version fails building due to having an older pytest configuration,
and this versions pypi release doesn't have the tests dir distributed in
the tarball anyways.

pkgs/applications/misc/octoprint/default.nix

@@ -15,13 +15,26 @@ let
     packageOverrides = lib.foldr lib.composeExtensions (self: super: { }) ([
       (mkOverride "flask"       "0.10.1" "0wrkavjdjndknhp8ya8j850jq7a1cli4g5a93mg8nh1xz2gq50sc")
       (mkOverride "flask_login" "0.2.11" "1rg3rsjs1gwi2pw6vr9jmhaqm9b3vc9c4hfcsvp4y8agbh7g3mc3")
-      (mkOverride "jinja2"      "2.8.1"  "14aqmhkc9rw5w0v311jhixdm6ym8vsm29dhyxyrjfqxljwx1yd1m")
       (mkOverride "pylru"       "1.0.9"  "0b0pq0l7xv83dfsajsc49jcxzc99kb9jfx1a1dlx22hzcy962dvi")
       (mkOverride "sarge"       "0.1.4"  "08s8896973bz1gg0pkr592w6g4p6v47bkfvws5i91p9xf8b35yar")
       (mkOverride "tornado"     "4.5.3"  "02jzd23l4r6fswmwxaica9ldlyc2p6q8dk6dyff7j58fmdzf853d")
 
       # https://github.com/NixOS/nixpkgs/pull/58179#issuecomment-478605134
       (mkOverride "werkzeug"    "0.14.1" "c3fd7a7d41976d9f44db327260e263132466836cef6f91512889ed60ad26557c")
+
+      # Octoprint holds back jinja2 to 2.8.1 due to breaking changes.
+      # This old version does not have updated test config for pytest 4,
+      # and pypi tarball doesn't contain tests dir anyways.
+      (pself: psuper: {
+        jinja2 = psuper.jinja2.overridePythonAttrs (oldAttrs: rec {
+          version = "2.8.1";
+          src = oldAttrs.src.override {
+            inherit version;
+            sha256 = "14aqmhkc9rw5w0v311jhixdm6ym8vsm29dhyxyrjfqxljwx1yd1m";
+          };
+          doCheck = false;
+        });
+      })
     ]);
   };