Alpine Base Image (#313)

- updating to the latest alpine release 3.7

CHANGELOG.md

 
+#### **2.1.2 (Unreleased)**
+
+FEATURES:
+* Updated the docker base image alpine 3.7 [#PR313](https://github.com/gambol99/keycloak-proxy/pull/313)
+
 #### **2.1.1**
 
 FEATURES:

Dockerfile

-FROM alpine:3.6
+FROM alpine:3.7
 MAINTAINER Rohith Jayawardene <gambol99@gmail.com>
 LABEL Name=keycloak-proxy \
       Release=https://github.com/gambol99/keycloak-proxy \