Update Dockerfile. Switch to Go 1.13 (#28)

Author: psampaz

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Run tests on Go 1.13
 
 ### Changed
+- Updated docker base image to 1.13.1
 - Replaced Travis with Github Actions
 - Updated version of golangci-lint to 1.18
 

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.12.7-alpine3.10
+FROM golang:1.13.1-alpine3.10
 RUN apk add --no-cache git
 WORKDIR /home
 COPY ./ .