Fix for Dockerfile smell DL4006

Hi! The Dockerfile placed at "Dockerfile" contains the best practice violation DL4006 detected by the hadolint tool.

The smell DL4006 occurs when there is a RUN instruction with a pipe in and the -o pipefail option is missing. The issue is that the RUN instruction only evaluates the exit code of the last operation in the pipe to determine success. Thus, during the Docker build, if one of the statements contained in the RUN instruction fails but not the last, the build will continue even if there is an error. This pull request proposes a fix for that smell generated by my fixing tool. The patch was manually verified before opening the pull request. To fix this smell, specifically, the option -o pipefail is placed before the RUN instruction with a pipe in.

This change is only aimed at fixing that specific smell. If the fix is not valid or useful, please briefly indicate the reason and suggestions for possible improvements.

Thanks in advance

omise / omise-python

Fix for Dockerfile smell DL4006 #62