title: build path either does not exist, is not accessible, or is not a valid URL
body: <p>I tryna figure out docker to run my django rest framework + vue.js project in clouds. I built Dockerfile and docker-compose.yml file to start an ubuntu machine and run the postgresql, vue.js and drf containers. But when I try run <code>docker-compose build</code> I get the following message:</p>
  <pre><code>build path either does not exist, is not accessible, or is not a valid URL
  </code></pre>
  <p>Here is my Dockerfile:</p>
  <pre><code>RUN apt-get update &amp;&amp; upt-get install -y \
      gcc \
      musl-dev \
      node.js \
      postgresql-server-dev-10 \
      apt-utils \
      python3.7 \
      python3.7-dev \
      python3-pip \
  &amp;&amp; apt-get clean \
  &amp;&amp; rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
  
  RUN npm install webpack@2.9
  
  WORKDIR /app
  
  COPY requirements.txt /app
  RUN pip3 install --no-cache-dir -r requirements.txt
  
  COPY . /app
  </code></pre>
  <p>docker-compose.yml:</p>
  <pre><code>version: '3.5'
  
  services:
    postgres:
      image: postgres:10
      environment:
        POSTGRES_USER: postgres
        POSTGRES_PASSWORD: 8599
        POSTGRES_DB: adserver
      volumes:
        - adserver-data/postgresql/data:/var/lib/postgresql/data
      restart: always
    rest_framework:
      build:
        context: ./app/adserver
        dockerfile: Dockerfile
      depends_on:
        - postgres
      command: ['python manage.py runserver']
      restart: always
    vue:
      build:
        context: ./app/adserver-vue
      depends_on:
        - rest_framework
      command: ['npm run watch']
  </code></pre>
  <p>Please tell me what am I doing wrong?</p>