build: yet another weird PPA fix

Author: karalabe

build/deb/ethereum/deb.rules

@@ -21,8 +21,8 @@ override_dh_auto_build:
 	# requirements opposed to older versions of Go.
 	(mv .goboot ../ && cd ../.goboot/src && ./make.bash)
 	export GOROOT_BOOTSTRAP=`pwd`/../.goboot
-	echo $GOROOT_BOOTSTRAP
-	(mv .go ../ && cd ../.go/src && ./make.bash)
+	echo $(GOROOT_BOOTSTRAP)
+	(mv .go ../ && cd ../.go/src && GOROOT_BOOTSTRAP=`pwd`/../../.goboot ./make.bash)
 
 	# We can't download external go modules within Launchpad, so we're shipping the
 	# entire dependency source cache with go-ethereum.