install git in travis so that branch releases can be used

Trying to use an pre-release version of node-data-tools, but yarn apparently
expects it can shell out to git in order to pull the branch.

Author: ewollesen

Dockerfile

@@ -3,7 +3,7 @@ FROM node:16.20.1-alpine as base
 WORKDIR /app
 RUN apk --no-cache update && \
     apk --no-cache upgrade && \
-    apk add --no-cache --virtual .build-dependencies python3 make g++ && \
+    apk add --no-cache --virtual .build-dependencies python3 make g++ git && \
     mkdir -p node_modules && chown -R node:node .