shell: Free temporary strings

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
diff --git a/src/shell.c b/src/shell.c
index ceb963c..4447995 100644
--- a/src/shell.c
+++ b/src/shell.c
@@ -402,8 +402,10 @@
 	weston_config_section_get_string(section,
 					 "binding-modifier", &s, "super");
 	shell->binding_modifier = get_modifier(s);
+	free(s);
 	weston_config_section_get_string(section, "animation", &s, "none");
 	shell->win_animation_type = get_animation_type(s);
+	free(s);
 	weston_config_section_get_uint(section, "num-workspaces",
 				       &shell->workspaces.num,
 				       DEFAULT_NUM_WORKSPACES);