Fix dorie.dockerfile

Merge delete command into single line because Docker does not accept
multi-line strings

docker/dorie.dockerfile

@@ -14,10 +14,7 @@ RUN CMAKE_FLAGS="-DCMAKE_BUILD_TYPE=Release -DCMAKE_C_COMPILER=${CC} -DCMAKE_CXX
     ./dune-common/bin/dunecontrol --only=dorie configure \
     && ./dune-common/bin/dunecontrol --only=dorie make -j ${PROCNUM} dorie-rfg dorie \
     && ./dune-common/bin/dunecontrol --only=dorie exec \
-        "rm build-cmake/dune/dorie/model/richards/impl/libdorie-richards.a 
-            build-cmake/dune/dorie/model/transport/impl/libdorie-transport.a 
-            build-cmake/dune/dorie/model/richards/impl/CMakeFiles/dorie-richards.dir/*.cc.o
-            build-cmake/dune/dorie/model/transport/impl/CMakeFiles/dorie-transport.dir/*.cc.o" 
+        "rm build-cmake/dune/dorie/model/richards/impl/libdorie-richards.a build-cmake/dune/dorie/model/transport/impl/libdorie-transport.a build-cmake/dune/dorie/model/richards/impl/CMakeFiles/dorie-richards.dir/*.cc.o build-cmake/dune/dorie/model/transport/impl/CMakeFiles/dorie-transport.dir/*.cc.o" 
 
 # move to working directory
 WORKDIR /mnt