Dockerfile: Add --with-iostreams to `boost` build process.

Would otherwise be missing and fails fresh install.

Docker/Dockerfile

@@ -31,7 +31,7 @@ RUN wget https://dl.bintray.com/boostorg/release/1.64.0/source/boost_1_64_0.tar.
     && ./bootstrap.sh --prefix=/usr/local \
     && echo 'using clang : 4.0 : clang++-4.0 ;' >> project-config.jam \
     && ./b2 -d0 -j4 --with-thread --with-date_time --with-system --with-filesystem --with-program_options \
-       --with-signals --with-serialization --with-chrono --with-test --with-context --with-locale --with-coroutine toolset=clang link=static install \
+       --with-signals --with-serialization --with-chrono --with-test --with-context --with-locale --with-coroutine --with-iostreams toolset=clang link=static install \
     && cd .. && rm -rf boost_1_64_0
 
 RUN wget https://github.com/mongodb/mongo-c-driver/releases/download/1.8.0/mongo-c-driver-1.8.0.tar.gz -O - | tar -xz \