[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/$VERSION.tar.gz && \
@@ -25,7 +26,7 @@ RUN addgroup --gid 5010 codimd && \
     mkdir -p /home/codimd/app && \
     chown -R codimd:codimd /home/codimd && \
     apk add --no-cache git bash python && \
-    wget https://github.com/hackmdio/portchecker/releases/download/v1.0.5/portchecker-linux-amd64.tar.gz && \
+    wget https://github.com/hackmdio/portchecker/releases/download/${PORTCHECKER_VERSION}/portchecker-linux-amd64.tar.gz && \
     tar xvf portchecker-linux-amd64.tar.gz -C /usr/local/bin && \
     mv /usr/local/bin/portchecker-linux-amd64 /usr/local/bin/pcheck && \
     rm portchecker-linux-amd64.tar.gz