- Next means - node:10.13.0use debian9, aka- stretch.
 - $ docker run --rm node:10.13.0 cat /etc/issue
Debian GNU/Linux 9 \n \l
 
- Next means - node:10.13.0default use- git 2.11.
 - $ docker run --rm node:10.13.0 git --version
git version 2.11.0
 
In fact, git in debian 9 apt repo use the version 2.11, if you want to upgrade to a newer version, you could use debian backports, which means:
Backports are packages taken from the next Debian release
By default, backports won't be used when use apt. You could use next sample to enable this.
Dockerfile:
FROM node:10.13.0
RUN echo "deb http://deb.debian.org/debian stretch-backports main contrib non-free" >> /etc/apt/sources.list; \
    apt-get update; \
    apt-get -t stretch-backports install git -y
Verify it:
$ docker build -t mynodeimage .
Sending build context to Docker daemon  2.048kB
Step 1/2 : FROM node:10.13.0
......
Successfully tagged mynodeimage:latest
$ docker run --rm mynodeimage git --version
git version 2.20.1