switched to milter-sasl release

milter-sasl/Dockerfile

     apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 RUN git clone https://git.rthoni.com/robin.thoni/milter-sasl &&\
-    cd milter-sasl && git checkout develop  &&\
+    cd milter-sasl &&\
     mkdir build && cd build &&\
     cmake .. && make &&\
     cp src/milter-sasl /usr/local/bin