Fix git commands (#1577)

advanced/Scripts/update.sh

@@ -40,7 +40,7 @@ GitCheckUpdateAvail() {
 
   # @ alone is a shortcut for HEAD. Older versions of git
   # need @{0}
-  LOCAL="$("git rev-parse @{0}")"
+  LOCAL="$(git rev-parse "@{0}")"
 
   # The suffix @{upstream} to a branchname
   # (short form <branchname>@{u}) refers
@@ -49,7 +49,7 @@ GitCheckUpdateAvail() {
   # (configured with branch.<name>.remote and
   # branch.<name>.merge). A missing branchname
   # defaults to the current one.
-  REMOTE="$("git rev-parse @{upstream}")"
+  REMOTE="$(git rev-parse "@{upstream}")"
 
   if [[ ${#LOCAL} == 0 ]]; then
     echo -e "        ${COL_LIGHT_RED}Error: Local revision could not be obtained, ask Pi-hole support."