Updated to esp-idf v4.0-rc

Dockerfile

@@ -4,6 +4,6 @@ RUN apt update \
  && DEBIAN_FRONTEND=noninteractive apt install git-core cmake libusb-1.0-0 python3 python-is-python3 python3-virtualenv ccache -y \
  && rm /var/lib/apt/lists/* /var/log/* -Rf
 
-RUN git clone --branch=v4.0-dev https://github.com/espressif/esp-idf.git esp-idf \
+RUN git clone --branch=v4.0-rc https://github.com/espressif/esp-idf.git esp-idf \
  && ./esp-idf/install.sh \
  && rm -Rf esp-idf