Update Dockerfile

Dockerfile

@@ -50,4 +50,6 @@ COPY --from=fat /usr/lib/x86_64-linux-gnu /usr/lib/x86_64-linux-gnu
 COPY --from=fat /usr/libexec /usr/libexec
 
 # Default to UTF-8 file.encoding
-ENV LANG='en_US.UTF-8' LANGUAGE='en_US:en' LC_ALL='en_US.UTF-8' TZ='UTC'
+ENV LANG='en_US.UTF-8' LANGUAGE='en_US:en' LC_ALL='en_US.UTF-8' TZ='UTC'
+
+RUN /bin/sh -c set -eux; echo "Verifying install ..."; fileEncoding="$(echo 'System.out.println(System.getProperty("file.encoding"))' | jshell -s -)"; [ "$fileEncoding" = 'UTF-8' ]; echo "Complete."