Update base image to alpine:3.12.6

Alpine 3.12.5 has a known vulnerability:
  High severity vulnerability found in busybox/busybox
  Description: Improper Handling of Exceptional Conditions
  Info: https://snyk.io/vuln/SNYK-ALPINE312-BUSYBOX-1089799
  Introduced through: busybox/busybox@1.31.1-r19, alpine-baselayout/alpine-baselayout@3.2.0-r7, busybox/ssl_client@1.31.1-r19
  From: busybox/busybox@1.31.1-r19
  From: alpine-baselayout/alpine-baselayout@3.2.0-r7 > busybox/busybox@1.31.1-r19
  From: busybox/ssl_client@1.31.1-r19
  Fixed in: 1.31.1-r20

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.12.5 AS stage
+FROM alpine:3.12.6 AS stage
 LABEL maintainer="Nicolas Favre-Felix <n.favrefelix@gmail.com>"
 
 RUN apk update && apk add wget make gcc libevent-dev msgpack-c-dev musl-dev bsd-compat-headers jq
@@ -9,7 +9,7 @@ RUN cd webdis-$(cat latest) && make && make install && cd ..
 RUN sed -i -e 's/"daemonize":.*true,/"daemonize": false,/g' /etc/webdis.prod.json
 
 # main image
-FROM alpine:3.12.5
+FROM alpine:3.12.6
 RUN apk update && apk add libevent msgpack-c redis       # Required dependencies
 RUN apk add libcrypto1.1                                 # Security updates
 COPY --from=stage /usr/local/bin/webdis /usr/local/bin/