Update xulrunner location

It recently changed after a gaia refactoring

Change-Id: Ie89c7f3eac229137318a797b3ecbeb92419ae2f5

vendorsetup.sh

@@ -261,7 +261,7 @@ else
 fi
 
 # Use a local Xulrunner SDK copy instead of downloading
-if [[ -d gaia/xulrunner-sdk/.git ]]; then
+if [[ -d gaia/xulrunner-sdk-26/.git ]]; then
    export USE_LOCAL_XULRUNNER_SDK=1
 fi