Fix Docker build

Dockerfile

@@ -3,8 +3,9 @@ RUN apt-get update -yq && apt-get upgrade -yq && apt-get install -yq curl git na
 RUN curl -sL https://deb.nodesource.com/setup_current.x | bash - && apt-get install -yq nodejs build-essential
 WORKDIR /app
 RUN apt-get install wget unzip -y
+RUN apt-get clean && rm -rf /var/lib/apt/lists/*
 RUN wget $(curl -s https://api.github.com/repos/openbullet/OpenBullet2/releases/latest | grep 'browser_' | cut -d\" -f4)
 RUN unzip OpenBullet2.zip
-RUN cp -r ./OpenBullet2/* . && rm -rf ./OpenBullet2 && rm OpenBullet2.zip
+RUN rm OpenBullet2.zip
 EXPOSE 5000
 CMD ["dotnet", "./OpenBullet2.dll", "--urls=http://*:5000"]