gluon-site: set PKG_FILE_DEPENDS to site.conf and i18n/ only

PKG_FILE_DEPENDS caused the whole site repo to be hashed to determine if
gluon-site needed rebuilding. While this is normally no problem,
alternative build setups sometimes put the Gluon repo inside the site repo,
causing long build times and parallel build failures.

package/gluon-site/Makefile

@@ -4,7 +4,7 @@ PKG_NAME:=gluon-site
 PKG_VERSION:=$(if $(GLUON_SITE_CODE),$(GLUON_SITE_CODE),1)
 PKG_RELEASE:=$(GLUON_RELEASE)
 
-PKG_FILE_DEPENDS := $(GLUON_SITEDIR)/
+PKG_FILE_DEPENDS := $(GLUON_SITEDIR)/site.conf $(GLUON_SITEDIR)/i18n/
 PKG_BUILD_DEPENDS := luci-base/host
 
 PKG_BUILD_DIR := $(BUILD_DIR)/$(PKG_NAME)