fix build arg [NVM_NODEJS_ORG_MIRROR] not consumed warning (laradock#2411)

Author: bestlong

workspace/Dockerfile

@@ -614,7 +614,8 @@ ARG INSTALL_NPM_ANGULAR_CLI=false
 ARG NPM_REGISTRY
 ENV NPM_REGISTRY ${NPM_REGISTRY}
 ENV NVM_DIR /home/laradock/.nvm
-ENV NVM_NODEJS_ORG_MIRROR=${NVM_NODEJS_ORG_MIRROR}
+ARG NVM_NODEJS_ORG_MIRROR
+ENV NVM_NODEJS_ORG_MIRROR ${NVM_NODEJS_ORG_MIRROR}
 
 RUN if [ ${INSTALL_NODE} = true ]; then \
     # Install nvm (A Node Version Manager)