[WM] switch to clojure-api base Docker image

It has leiningen in it now because we stopped using the old one that didn't
and instead were using "clojure-api-build" for runtime, which didn't really
make sense.
Merge pull request #5 from votinginfoproject/switch-to-clojure-api-base-image

[WM] switch to clojure-api base Docker image