Update Dockerfile

Dockerfile

@@ -5,8 +5,9 @@ RUN apt install git -y
 
 RUN apt-get install build-essential cmake git libjson-c-dev libwebsockets-dev -y
 RUN git clone https://github.com/tsl0922/ttyd.git
-
-RUN cd ttyd && mkdir build && cd build
+WORKDIR ttyd/
+RUN mkdir build 
+WORKDIR build/
 RUN cmake ..
 RUN make && make install
 CMD ["ttyd", "-p", "8080", "bash"]