chore: update git (#150)

* chore: rename image name
* chore: add git v2.25.0
* chore: enhance Dockerfile

__tests__/Dockerfile

@@ -1,11 +0,0 @@
-FROM node:12-slim
-
-WORKDIR /repo
-
-RUN apt-get update && \
-    apt-get -y install --no-install-recommends \
-    git \
-    bash && \
-    rm -rf /var/lib/apt/lists/*
-
-CMD [ "bash" ]