E: oracle-java8-installer 패키지를 찾을 수 없습니다.

저는 java8을 설치하기 위해 다음 Dockerfile을 사용하고 있습니다. 그런데 도커 이미지를 생성하는 중에 갑자기 오류가 발생했습니다.

E: Unable to locate package oracle-java8-installer
E: Unable to locate package oracle-java8-set-default

도커파일

FROM ubuntu:trusty-20151218

ENV JAVA_VER 8
ENV JAVA_HOME /usr/lib/jvm/java-8-oracle

RUN echo 'deb http://ppa.launchpad.net/webupd8team/java/ubuntu trusty main' >> /etc/apt/sources.list && \
    echo 'deb-src http://ppa.launchpad.net/webupd8team/java/ubuntu trusty main' >> /etc/apt/sources.list && \
    apt-key adv --keyserver keyserver.ubuntu.com --recv-keys C2518248EEA14886 && \
    apt-get update && \
    echo oracle-java${JAVA_VER}-installer shared/accepted-oracle-license-v1-1 select true | sudo /usr/bin/debconf-set-selections && \
    apt-get install -y --force-yes --no-install-recommends oracle-java${JAVA_VER}-installer oracle-java${JAVA_VER}-set-default && \
    rm -rf /var/cache/oracle-jdk${JAVA_VER}-installer \
    echo 'APT::Install-Recommends 0;' >> /etc/apt/apt.conf.d/01norecommends \
    && echo 'APT::Install-Suggests 0;' >> /etc/apt/apt.conf.d/01norecommends \
    && DEBIAN_FRONTEND=noninteractive apt-get install -y vim.tiny wget sudo net-tools ca-certificates unzip \
    && apt-get clean \
    && rm -rf /var/lib/apt/lists/*