gapps: Update date format

* Use UTC
* Don't put hypens everywhere

build/gapps.sh

@@ -6,7 +6,7 @@
 ##
 # var
 #
-DATE=$(date +%F-%H-%M)
+DATE=$(date -u +%Y%m%d_%H%M%S)
 TOP=$(realpath .)
 ANDROIDV=8.1.0
 GARCH=$1