Warn when aur repo -u fails

Print a warning instead of silently counting 0 AUR updates, and stop
discarding aur's stderr so the cause shows up in the journal.

update-notify

@@ -88,7 +88,11 @@ arch_updates=${#arch_list[@]}
 
 aur_updates=0
 if command -v aur >/dev/null 2>&1; then
-    aur_updates=$(aur repo -u -d "$AUR_REPO" 2>/dev/null | wc -l)
+    if aur_out=$(aur repo -u -d "$AUR_REPO"); then
+        [[ -n $aur_out ]] && aur_updates=$(wc -l <<< "$aur_out")
+    else
+        echo "aur repo -u failed, AUR updates not counted" >&2
+    fi
 fi
 updates=$((arch_updates + aur_updates))