[CodiMD] Bump portchecker version and use env variable in Dockerfile

pica-codimd/Dockerfile

 FROM node:10.22.1-alpine3.11 as BUILD
 
 ENV VERSION=2.2.0
+ENV PORTCHECKER_VERSION=v1.0.6
 
 RUN apk add --no-cache --virtual .gyp libressl-dev git bash python make && \
 wget https://github.com/hackmdio/codimd/archive/$VERSION.tar.gz && \