Update Dockerfile, add libass

Dockerfile

@@ -60,6 +60,7 @@ RUN apt-get upgrade -y \
 		gcc-mingw-w64 \
 		libz-mingw-w64 \
 		cmake \
+		libass-dev \
 	&& rm -rf /var/lib/apt/lists/*
 
 RUN echo "###### Ubuntu Main Repos" > /etc/apt/sources.list && \