Add :preamble

Since https://github.com/clojure/clojurescript/commit/136bf46c656265a93dd15c40925f11edb34bd127 the Clojurescript compiler supports :preamble
Merge pull request #311 from paulbutcher/patch-2

Add :preamble to sample.project.clj
Update plugin dependency to 1.0.3
Merge pull request #314 from wtfleming/patch-1

Update plugin dependency shown in sample.project.clj to 1.0.3
Merge branch 'master' into patch-1

Conflicts:
	sample.project.clj