[gnome-software] trivial: Fix make check failure after recent error enum addition

[Richard Hughes <rhughes src gnome org>]

commit 5627dc41d53208d830693b35ebba7cdb0317d01c
Author: Richard Hughes <richard hughsie com>
Date:   Wed Dec 21 15:56:57 2016 +0000

    trivial: Fix make check failure after recent error enum addition

 src/gs-plugin.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/src/gs-plugin.c b/src/gs-plugin.c
index 8b22232..13fa242 100644
--- a/src/gs-plugin.c
+++ b/src/gs-plugin.c
@@ -1417,6 +1417,8 @@ gs_plugin_error_to_string (GsPluginError error)
                return "delete-failed";
        if (error == GS_PLUGIN_ERROR_RESTART_REQUIRED)
                return "restart-required";
+       if (error == GS_PLUGIN_ERROR_AC_POWER_REQUIRED)
+               return "ac-power-required";
        return NULL;
 }