Fix Dockerfile having no workdir set

Author: nurupo

other/docker/windows/Dockerfile

@@ -16,6 +16,8 @@ ENV SUPPORT_ARCH_i686=${SUPPORT_ARCH_i686}
 ENV SUPPORT_ARCH_x86_64=${SUPPORT_ARCH_x86_64}
 ENV CROSS_COMPILE=${CROSS_COMPILE}
 
+WORKDIR /
+
 COPY get_packages.sh .
 RUN sh ./get_packages.sh