Optimize dockerfile

Dockerfile

@@ -1,12 +1,29 @@
+# Build
 FROM microsoft/dotnet:2.1-sdk AS build
 WORKDIR /src
+
+COPY favicon.ico ./
+
+COPY DiscordChatExporter.Core.Markdown/*.csproj DiscordChatExporter.Core.Markdown/
+RUN dotnet restore DiscordChatExporter.Core.Markdown
+
+COPY DiscordChatExporter.Core/*.csproj DiscordChatExporter.Core/
+RUN dotnet restore DiscordChatExporter.Core
+
+COPY DiscordChatExporter.Cli/*.csproj DiscordChatExporter.Cli/
+RUN dotnet restore DiscordChatExporter.Cli
+
 COPY DiscordChatExporter.Core.Markdown DiscordChatExporter.Core.Markdown
 COPY DiscordChatExporter.Core DiscordChatExporter.Core
 COPY DiscordChatExporter.Cli DiscordChatExporter.Cli
-COPY DiscordChatExporter.sln favicon.ico ./
+
 RUN dotnet build DiscordChatExporter.Cli -c Release -f netcoreapp2.1
 
-FROM build AS app
+# Run
+FROM microsoft/dotnet:2.1-runtime AS run
 WORKDIR /app
+
 COPY --from=build /src/DiscordChatExporter.Cli/bin/Release/netcoreapp2.1 ./
-ENTRYPOINT ["dotnet", "DiscordChatExporter.Cli.dll"]
+
+ENTRYPOINT ["dotnet", "DiscordChatExporter.Cli.dll"]
+CMD ["-o", "out/"]