Dockercompose utilizando proxy | Docker: Criando containers sem dor de cabeça

Seguindo a aula 06, comecei criando apenas um nó do sistema, para o node1. Escrevi o seguinte docker-compose.yml:

version: '3'

networks:
  production-network:
    driver: bridge

services:
  node1:
    build:
      dockerfile: ./docker/alura-books.dockerfile
      context: .
    image: giulianasilvabezerra/alura-books
    container_name: alura-books-1
    ports:
      - "3000"
    networks:
      - production-network

Para construir o meu serviço, tenho o seguinte Dockerfile:

FROM node:latest
MAINTAINER Douglas Quintanilha
ENV NODE_ENV=development
COPY . /var/www
WORKDIR /var/www
RUN npm install 
ENTRYPOINT ["npm", "start"]
EXPOSE 3000

Como utilizo um proxy coorporativo, pesquisei um jeito de informá-lo para o build dessa imagem, e verifiquei que isso seria possível com o npm config. Então, adicionei os comandos:

RUN npm cache clean -f
RUN npm config set proxy http://10.100.5.107:3128
RUN npm config set https-proxy http://10.100.5.107:3128
RUN npm update
RUN npm install

Ond 10.100.5.107 é o ip da minha máquina que serve de proxy na porta 3128, sem autenticação requerida. O problema é que quando tento rodar o build, ocorre erro devido a essa configuração de proxy:

docker-compose build
Building node1
Step 1/12 : FROM node:latest ---> 8672b25e842c
Step 2/12 : MAINTAINER Douglas Quintanilha ---> Using cache
 ---> 57cc55c8c60a
Step 3/12 : ENV NODE_ENV=development
 ---> Using cache
 ---> ad9c7e8d30c1
Step 4/12 : COPY . /var/www
 ---> aec64fdc16ae
Step 5/12 : WORKDIR /var/www
 ---> Running in d1121964dbe4
Removing intermediate container d1121964dbe4
 ---> 78f225a89e7d
Step 6/12 : RUN npm cache clean -f
 ---> Running in f84cd3c05903
npm WARN using --force I sure hope you know what you are doing.
Removing intermediate container f84cd3c05903
 ---> ec8d4392504e
Step 7/12 : RUN npm config set proxy http://localhost:3128
 ---> Running in 1d9af892155c
Removing intermediate container 1d9af892155c
 ---> 71813002714c
Step 8/12 : RUN npm config set https-proxy http://localhost:3128
 ---> Running in 3d9376ff8574
Removing intermediate container 3d9376ff8574 ---> a74660004639
Step 9/12 : RUN npm update
 ---> Running in 1af0de20e9e2
npm ERR! code ECONNRESET
npm ERR! network tunneling socket could not be established, cause=connect ECONNREFUSED 127.0
.0.1:3128
npm ERR! network This is a problem related to network connectivity.
npm ERR! network In most cases you are behind a proxy or have bad network settings.
npm ERR! network
npm ERR! network If you are behind a proxy, please make sure that the
npm ERR! network 'proxy' config is set properly.  See: 'npm help config'

npm ERR! A complete log of this run can be found in:
npm ERR!     /root/.npm/_logs/2018-10-01T15_32_58_226Z-debug.log
ERROR: Service 'node1' failed to build: The command '/bin/sh -c npm update' returned a non-z
ero code: 1

Como eu deveria configurar o proxy para o build dessa imagem no docker-compose? Já procurei em vários tutoriais, mas não obtive sucesso.

OBS:

Máquina: Ubuntu 18
Docker version 18.06.1-ce
docker-compose version 1.15.0, build e12f3b9