[#999] Remove cljsbuild clean from update process

* https://github.com/emezeske/lein-cljsbuild/commit/12e9955b3f37ee4c1daa15665cafbf6f5e6433fe
Merge pull request #1000 from akvo/issue/999-remove-cljsbuild-clean

[#999] Remove cljsbuild clean from update process