[nix] don't use experimental features for corenlp nix call

Also, update Dockerfile with patched `nix.conf`

devops/docker/Dockerfile

@@ -35,9 +35,10 @@ SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 
 RUN set -o pipefail && \
     locale-gen en_US.UTF-8 && \
-    bash <(curl -L https://releases.nixos.org/nix/nix-2.26.2/install) --no-daemon && \
+    bash <(curl -L https://releases.nixos.org/nix/nix-2.26.3/install) --no-daemon && \
     chown root -R /nix && \
     . "$HOME/.nix-profile/etc/profile.d/nix.sh" && \
+    mkdir -vp "$HOME/.config/nix" && echo "experimental-features = nix-command flakes" >> $HOME/.config/nix/nix.conf && \
     mkdir -p "/builds/gargantext/" && chmod 777 -R "/builds/gargantext" && \
     echo "source $HOME/.nix-profile/etc/profile.d/nix.sh" >> "$HOME/.bashrc" && \
     echo `which nix-env` && \

test/drivers/hspec/Main.hs

@@ -21,9 +21,7 @@ startCoreNLPServer :: IO ProcessHandle
 startCoreNLPServer = do
   putText "calling start core nlp"
   devNull <- openFile "/dev/null" WriteMode
-  let p = proc "nix" [ "--experimental-features"
-                     , "nix-command flakes"
-                     , "run"
+  let p = proc "nix" [ "run"
                      , "git+https://gitlab.iscpif.fr/gargantext/corenlp-nix.git" ]
   (_, _, _, hdl) <- (createProcess $ p { cwd = Nothing
                     -- NOTE(adn) Issue #451, this one has to stay disabled, because if we