Fixed git checkout

Dockerfile

@@ -1,6 +1,6 @@
 from debian as build-rtl_433
-RUN apt-get update && apt-get upgrade -y 
-RUN apt-get install -y libtool libusb-1.0.0-dev librtlsdr-dev rtl-sdr build-essential autoconf cmake pkg-config git && apt-get clean
+RUN apt-get update && apt-get upgrade -y && apt-get clean
+RUN apt-get update && apt-get install -y libtool libusb-1.0.0-dev librtlsdr-dev rtl-sdr build-essential autoconf cmake pkg-config git && apt-get clean
 RUN git clone https://github.com/merbanan/rtl_433.git
 WORKDIR /rtl_433
 RUN mkdir -p build