yarn-config-hook: use $TMP instead of /tmp

$TMP should be univsal for all derivations and should
work on darwin as well, if it ever switches to another
build-dir (e.g. /nix/)

see NixOS#355053 (comment)

Signed-off-by: Florian Brandes <florian.brandes@posteo.de>

pkgs/build-support/node/fetch-yarn-deps/yarn-config-hook.sh

@@ -2,8 +2,8 @@ yarnConfigHook(){
     echo "Executing yarnConfigHook"
 
     # Use a constant HOME directory
-    mkdir -p /tmp/home
-    export HOME=/tmp/home
+    mkdir -p $TMP/home
+    export HOME=$TMP/home
     if [[ -n "$yarnOfflineCache" ]]; then
         offlineCache="$yarnOfflineCache"
     fi