Change Docker build context to repo root

[4310V343k]

When rebuilding a container, it would be very nice to have the root of the repository set as the root of the Docker build context. So, instead of the command looking like this
docker build -f /path/to/repo/reponame/.devcontainer/Dockerfile -t vsc-*** /path/to/repo/reponame/.devcontainer
It would look like this
docker build -f /path/to/repo/reponame/.devcontainer/Dockerfile -t vsc-*** /path/to/repo/reponame

This will allow us to get versions of dependencies from the repo, for example a dependencies.sh file

Example

COPY dependencies.sh .

RUN . ./dependencies.sh \
	&& curl "http://www.byond.com/download/build/${BYOND_MAJOR}/${BYOND_MAJOR}.${BYOND_MINOR}_byond_linux.zip" -o byond.zip \
	&& unzip byond.zip \
	&& cd byond \
	&& make install \
	&& apt-get purge -y --auto-remove curl unzip make \
	&& cd .. \
	&& rm -rf byond byond.zip