build: target for go library dependencies

Didn't notice it because vendor/ was already populated on my dev
machine, but did notice it in Docker build.

Docker build now consumes devsetup like regular user, so this should
catch future problems.

Remove remaining curl|shit functionality from lazy.sh (no checkout logic
needed anymore).

refs #35

build.Dockerfile

@@ -1,20 +1,16 @@
 FROM golang:latest
 
-# Docs deps
 RUN apt-get update && apt-get install -y \
     python3-pip
 
 ADD lazy.sh /tmp/lazy.sh
-
-RUN /tmp/lazy.sh builddep
-
 ADD docs/requirements.txt /tmp/requirements.txt
 ENV ZREPL_LAZY_DOCS_REQPATH=/tmp/requirements.txt
-RUN /tmp/lazy.sh docdep
+RUN /tmp/lazy.sh devsetup
 
+# prepare volume mount of git checkout to /zrepl
 RUN mkdir -p /go/src/github.com/zrepl
-RUN ln -sf /zrepl /go/src/github.com/zrepl/zrepl
-
+RUN chmod -R 0777 /go
 WORKDIR /go/src/github.com/zrepl/zrepl