Updates.

- Newer Alpine image.
- Newer Hadolint.
- Newer dockerfile_lint.

Dockerfile

-FROM alpine:3.10
+FROM alpine:3.12
 # hadolint ignore=DL3016,DL3018
 RUN apk add --update --no-cache --repository http://dl-cdn.alpinelinux.org/alpine/edge/testing/ \
         docker-compose \
         npm \
     && \
     docker-compose --version && \
-    wget https://github.com/projectatomic/dockerfile_lint/archive/v0.3.3.tar.gz -O /tmp/dockerfile_lint.tar.gz && \
+    wget https://github.com/projectatomic/dockerfile_lint/archive/v0.3.4.tar.gz -O /tmp/dockerfile_lint.tar.gz && \
     npm install --global /tmp/dockerfile_lint.tar.gz && \
     install -d -o root -g root -m 755 /sample_rules && \
     tar -xzf /tmp/dockerfile_lint.tar.gz -C /tmp/ && \
     cp /tmp/dockerfile_lint*/sample_rules/*.yaml /sample_rules/ && \
     rm -rf /tmp/dockerfile_lint* && \
     dockerfile_lint --help && \
-    wget https://github.com/hadolint/hadolint/releases/download/v1.17.1/hadolint-Linux-x86_64 -O /usr/local/bin/hadolint && \
+    wget https://github.com/hadolint/hadolint/releases/download/v1.19.0/hadolint-Linux-x86_64 -O /usr/local/bin/hadolint && \
     chmod +x /usr/local/bin/hadolint && \
     hadolint --version
 COPY docker-compose-config dockerfile-lint /usr/local/bin/