fix bug in cache_dir

bin/compile

@@ -146,7 +146,7 @@ bpwatch stop clear_old_venvs
 
 # Restore old artifacts from the cache.
 bpwatch start restore_cache
-  mkdir -p $CACHEDIR/$CACHED_DIR
+  mkdir -p $CACHE_DIR/$CACHED_DIR
   for dir in $CACHED_DIRS; do
     cp -R $CACHE_DIR/$dir . &> /dev/null || true
   done