Fix session start with readPref

Author: kay-kim

source/includes/driver-examples/driver-example-transactions-retry-3.rst

@@ -67,7 +67,7 @@
             }
 
             // Start a session.
-            session = db.getMongo().startSession( { mode: "primary" } );
+            session = db.getMongo().startSession( { readPreference: { mode: "primary" } } );
 
             try{
                runTransactionWithRetry(updateEmployeeInfo, session);

source/reference/method/Session.abortTransaction.txt

@@ -166,7 +166,7 @@ or in committing the transaction, the session aborts the transaction.
    } // End of updateEmployeeInfo function
 
    // Start a session.
-   session = db.getMongo().startSession( { mode: "primary" } );
+   session = db.getMongo().startSession( { readPreference: { mode: "primary" } } );
 
    try{
       runTransactionWithRetry(updateEmployeeInfo, session);

source/reference/method/Session.commitTransaction.txt

@@ -148,7 +148,7 @@ as a single transaction.
    }
 
    // Start a session.
-   session = db.getMongo().startSession( { mode: "primary" } );
+   session = db.getMongo().startSession( { readPreference: { mode: "primary" } } );
 
    try{
       runTransactionWithRetry(updateEmployeeInfo, session);

source/reference/method/Session.startTransaction.txt

@@ -220,7 +220,7 @@ as a single transaction.
    }
 
    // Start a session.
-   session = db.getMongo().startSession( { mode: "primary" } );
+   session = db.getMongo().startSession( { readPreference: { mode: "primary" } } );
 
    try{
       runTransactionWithRetry(updateEmployeeInfo, session);