SERVER-36732 amend write

jstests/replsets/libs/election_handoff.js

@@ -46,7 +46,7 @@ var ElectionHandoffTest = (function() {
         // make sure that the primary is aware that the secondaries are ready and caught up
         // to the primary's lastApplied, so we issue a dummy write and wait on its optime.
         assert.writeOK(primary.getDB("test").secondariesMustBeCaughtUpToHere.insert(
-            {"a": 1}, {w: rst.nodes.length}));
+            {"a": 1}, {writeConcern: {w: rst.nodes.length}}));
         rst.awaitNodesAgreeOnAppliedOpTime();
 
         // Step down the current primary.