moves cache storage until after the post_compile hook.

bin/compile

@@ -169,12 +169,6 @@ source $BIN_DIR/steps/collectstatic
 # ### Finalize
 #
 
-# Store new artifacts in cache.
-for dir in $CACHED_DIRS; do
-  rm -rf $CACHE_DIR/$dir
-  cp -R $dir $CACHE_DIR/
-done
-
 # Set context environment variables.
 set-env PATH '$HOME/.heroku/python/bin:$PATH'
 set-env PYTHONUNBUFFERED true
@@ -189,6 +183,12 @@ set-default-env PYTHONPATH /app/
 # Experimental post_compile hook.
 source $BIN_DIR/steps/hooks/post_compile
 
+# Store new artifacts in cache.
+for dir in $CACHED_DIRS; do
+  rm -rf $CACHE_DIR/$dir
+  cp -R $dir $CACHE_DIR/
+done
+
 # ### Fin.
 
 deep-mv $BUILD_DIR $ORIG_BUILD_DIR