Don't dexpreopt gapps

This is done to reduce size of gapps in system.
First boot will take a little bit more.
diff --git a/gapps.mk b/gapps.mk
index 4b31b04..6697b81 100644
--- a/gapps.mk
+++ b/gapps.mk
@@ -1,4 +1,5 @@
 GAPPS_VARIANT := nano
+DONT_DEXPREOPT_PREBUILTS := true
 GAPPS_FORCE_PACKAGE_OVERRIDES := true
 GAPPS_FORCE_BROWSER_OVERRIDES := true
 GAPPS_FORCE_WEBVIEW_OVERRIDES := true