Fix nodesource link

Author: c-w

Dockerfile

@@ -4,7 +4,7 @@ FROM python:${PYTHON_VERSION}-stretch AS builder
 ARG NODE_VERSION="8.x"
 RUN curl -sL "https://deb.nodesource.com/setup_${NODE_VERSION}" | bash - \
  && apt-get install --no-install-recommends -y \
-      nodejs
+      nodejs=8.16.1-1nodesource1
 
 COPY tools/install-mssql.sh /doccano/tools/install-mssql.sh
 RUN /doccano/tools/install-mssql.sh --dev