Makefile: Disable parallel make.

Because many dependencies are missing, it is not safe to run parallel make. Alternately, this could be fixed by adding the missing dependencies, but that would be a larger change; and it seems to be planned that the Makefile be phased out anyway.

Fixes issue #201 .

Makefile

@@ -16,6 +16,7 @@ git_bin = $(shell which git)
 webpack_port = $(shell cat webpack_port 2>/dev/null || echo '3808')
 all: gitlab-setup gitlab-shell-setup gitlab-workhorse-setup support-setup gitaly-setup
+.NOTPARALLEL:
 # Set up the GitLab Rails app