reduces stream operations 2

ff/WavefrontSerializer.cpp

@@ -30,8 +30,7 @@ std::ostream& serialize_as_wavefront(std::ostream& out, const ff::Polyhedron* po
     for (auto& poly : polyhedron->topology().faces) {
         if (poly.vertexIndices.size() == 0)
             continue;
-        out << "f"
-            << " ";
+        out << "f ";
         for (size_t i = 0; i < poly.vertexIndices.size(); i++) {
             out << poly.vertexIndices[i] + 1;
             out << (i == poly.vertexIndices.size() - 1 ? "\n" : " ");