Update pipenv package installation

Add `pipenv check` to ensure that any PEP 508 requirements are met and
to check for any security vulnerabilities in the lock file
configuration. Replace `pipenv sync` with `pipenv install --deploy`.
They will both install all of the packages specified in the
Pipfile/Pipfile.lock files but the new method will ensure that the
Pipfile and Pipfile.lock files are in sync.

Dockerfile

@@ -63,7 +63,8 @@ RUN python3 -m pip install --no-cache-dir --upgrade pipenv==${PYTHON_PIPENV_VERS
 # Install code-gov-update Python requirements
 WORKDIR /tmp
 COPY src/Pipfile src/Pipfile.lock ./
-RUN pipenv sync --clear --verbose
+RUN pipenv check --verbose \
+  && pipenv install --clear --deploy --verbose
 
 # The version of Python used here should match the version of the Alpine
 # python3 package installed in the compile-stage.