Fix/sphinx doc for swift

docker-files/bc-dev-debian9

@@ -23,7 +23,8 @@ RUN apt-get update && \
 RUN apt-get update && \
     apt-get install -y alien at autoconf bison ccache clang cmake doxygen elfutils g++ gdb git graphviz intltool libtool lsb-release make nasm ninja-build openssh-client patch python3 python3-pip python3-pystache python3-six yasm && \
     apt-get clean && \
-    pip install sphinx javasphinx sphinx_csharp anarchy_sphinx
+    update-alternatives --install /usr/bin/python python /usr/bin/python3 1 && \
+    pip3 install sphinx javasphinx sphinx_csharp anarchy_sphinx
 
 # Install linphone & flexisip dependencies development packages
 RUN apt-get update && \