fix typo

spoke/Dockerfile

@@ -5,7 +5,7 @@ RUN echo "PermitRootLogin no" >> /etc/ssh/sshd_config
 RUN echo "PasswordAuthentication no" >> /etc/ssh/sshd_config
 RUN echo "Subsystem sftp internal-sftp" >> /etc/ssh/sshd_config
 
-RG UID=1000
+ARG UID=1000
 ARG GID=1000
 RUN groupadd -g ${GID} armbian && useradd -m -u ${UID} -g armbian armbian
 USER armbian