Fixed Haskell Dockerfile Linter issues

Necessary to address linter errors. The DL3008 warning is ignored since we don't want to pin package version at the moment (this might change in the future). This also ensures strict Bash usage is applied throughout the `Dockerfile` via the `SHELL` directive.

Milestone: patch

.hadolint.yml

@@ -0,0 +1,2 @@
+ignored:
+  - DL3008

Dockerfile

@@ -22,10 +22,9 @@ ENV BUNDLE_WITHOUT="development:quality:test:tools"
 
 WORKDIR /app
 
+SHELL ["/bin/bash", "-o", "errexit", "-o", "nounset", "-o", "pipefail", "-c"]
+
 RUN <<STEPS
-  set -o errexit
-  set -o nounset
-  set -o xtrace
   apt-get update -qq
   apt-get install --no-install-recommends -y \
   chromium \