fix manifest generation

was in wrong directory and missed GLUON_BRANCH

build.sh

@@ -114,7 +114,9 @@ progress "Assembling images.7z ..."
 
 # generate and copy manifest
 progress "Generating and copying manifest ..."
-make manifest || abort "Failed to generate the manifest, try running 'make manifest' in '$CODE_DIR' directory manually."
+pushd $CODE_DIR
+GLUON_BRANCH=$BRANCH make manifest || abort "Failed to generate the manifest, try running 'make manifest' in '$CODE_DIR' directory manually."
+popd
 cp "${CODE_DIR}/images/sysupgrade/${BRANCH}.manifest" "output/${BRANCH}/"
 
 # write (copy) version file