Fix aug_save() test

Author: raphink

tests/root/etc/passwd

@@ -1,4 +1,4 @@
-root:x:0:0:root:/root:/bin/bash
+root:x:0:0:root:/root:/bin/zsh
 bin:x:1:1:bin:/bin:/sbin/nologin
 daemon:x:2:2:daemon:/sbin:/sbin/nologin
 adm:x:3:4:adm:/var/adm:/sbin/nologin

tests/test.auglua

@@ -59,7 +59,9 @@ assert(aug_get("$raphink") == "314")
 --- assert(aug_get("$gid") == nil)
 
 --- test aug_save()
---- expect error here!
+--- reload tree to be clean
+aug_load()
+aug_set("etc/passwd/root/shell", "/bin/zsh")
 aug_save()
 
 --- test aug_load()