FAB-5634 Update Makefile for examples/cluster

configtxgen has been moved to a new location so
need to update the Makefile for examples/cluster

Change-Id: I9fbb86745015563c8f47ff0ca2d00060d32a9c86
Signed-off-by: Gari Singh <gari.r.singh@gmail.com>

Author: mastersingh24

examples/cluster/Makefile

@@ -43,7 +43,7 @@ CONFIGTXGEN=build/bin/configtxgen
 
 FABRICPKG=github.com/hyperledger/fabric
 pkgmap.cryptogen      := $(FABRICPKG)/common/tools/cryptogen
-pkgmap.configtxgen    := $(FABRICPKG)/common/configtx/tool/configtxgen
+pkgmap.configtxgen    := $(FABRICPKG)/common/tools/configtxgen
 
 help:
 	@cat usage.txt