anchor.diff:  
   # download and install Gradle
   # https://services.gradle.org/distributions/
  -ENV GRADLE_VERSION 4.10.3
  +ARG GRADLE_VERSION=4.10.3
   RUN cd /opt && \
       wget -q https://services.gradle.org/distributions/gradle-${GRADLE_VERSION}-bin.zip && \
       unzip gradle*.zip && \
  
positive.code: 
  # download and install Android SDK
  # https://developer.android.com/studio/#downloads
  ENV ANDROID_SDK_VERSION 4333796
  RUN mkdir -p /opt/android-sdk && cd /opt/android-sdk && \
      wget -q https://dl.google.com/android/repository/sdk-tools-linux-${ANDROID_SDK_VERSION}.zip && \
      unzip *tools*linux*.zip && \
  
negative.code: 
  # download and install Kotlin compiler
  # https://github.com/JetBrains/kotlin/releases/latest
  ARG KOTLIN_VERSION=1.3.11
  RUN cd /opt && \
      wget -q https://github.com/JetBrains/kotlin/releases/download/v${KOTLIN_VERSION}/kotlin-compiler-${KOTLIN_VERSION}.zip && \
      unzip *kotlin*.zip && \
  