hack: add `vim` to dlv image

by setting the EDITOR environment variable, and having `vim` installed,
we're able to jump from the view of a frame to the source code "like
magic"

Signed-off-by: Ciro S. Costa <cscosta@pivotal.io>

hack/dlv/Dockerfile

@@ -1,5 +1,8 @@
 FROM concourse/concourse:local
 
+ENV EDITOR=vim
+
+RUN apt install -y vim
 RUN go get -u -v github.com/go-delve/delve/cmd/dlv
 
 ENTRYPOINT [ "dlv" ]