changing base image to use updated libssl, adding tests to run --help for nu

Signed-off-by: Vanessa Sochat <vsochat@stanford.edu>

docker/Dockerfile

@@ -1,8 +1,9 @@
-ARG  FROMTAG=latest
+ARG FROMTAG=latest
 FROM quay.io/nushell/nu-base:${FROMTAG} as base
-FROM rust:1.37-slim
+FROM ubuntu:18.04
 COPY --from=base /usr/local/bin/nu /usr/local/bin/nu
-RUN apt-get update && \
-    apt-get install -y pkg-config libssl-dev
+ENV DEBIAN_FRONTEND noninteractive
+RUN apt-get update && apt-get install -y libssl-dev \
+    pkg-config
 ENTRYPOINT ["nu"]
 CMD ["-l", "info"]

docker/Dockerfile.nu-base

@@ -6,8 +6,6 @@ FROM ubuntu:16.04
 ENV DEBIAN_FRONTEND noninteractive
 RUN apt-get update && apt-get install -y libssl-dev \
     libxcb-composite0-dev \
-    libx11-dev \
-    libssl-dev \
     pkg-config \
     curl