update dockerfile to use the latest sdk

Author: davidwuya

Dockerfile

@@ -15,7 +15,7 @@ RUN apk update && \
 
 # Raspberry Pi Pico SDK
 ARG SDK_PATH=/usr/share/pico_sdk
-RUN git clone --depth 1 --branch 1.5.0 https://github.com/raspberrypi/pico-sdk $SDK_PATH && \
+RUN git clone --depth 1 --branch master https://github.com/raspberrypi/pico-sdk $SDK_PATH && \
     cd $SDK_PATH && \
     git submodule update --init