Upgrade nlohmann

Current version of nlohmann has some issues with c++20.  Upgrade it.

Tested:
Built bmcweb with
https://gerrit.openbmc-project.xyz/c/openbmc/entity-manager/+/47575 and
build succeeded.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: Ia8c42f8901b0e3ef613a0fe66ee92742d1680b6c
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index 3007ce1..ee3c936 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -132,7 +132,7 @@
     ),
     # Release 2020-08-06
     "nlohmann/json": PackageDef(
-        rev="v3.9.1",
+        rev="v3.10.4",
         build_type="cmake",
         config_flags=["-DJSON_BuildTests=OFF"],
         custom_post_install=[