Update Dockerfile (#1098)

Adds git to the build, this may increase the build size.

https://cloud.docker.com/u/parseplatform/repository/registry-1.docker.io/parseplatform/parse-server/builds/112a03a6-ef2e-4c6b-bb8f-9802aca574a9

Author: dplewis

Dockerfile

@@ -2,6 +2,9 @@
 # --- Base Node Image ---
 FROM node:8-alpine AS base
 
+RUN apk update; \
+  apk add git;
+
 WORKDIR /src
 
 # Copy package.json first to benefit from layer caching