Fix typo in test comments

Author: jeffycyang

test/functional/operation_example_tests.js

@@ -3897,7 +3897,7 @@ exports.shouldCorrectlyDropTheDatabase = {
         db.dropDatabase(function(err, result) {
           test.equal(null, err);
 
-          // Wait to seconds to let it replicate across
+          // Wait two seconds to let it replicate across
           setTimeout(function() {
             // Get the admin database
             db.admin().listDatabases(function(err, dbs) {

test/functional/operation_generators_example_tests.js

@@ -3290,7 +3290,7 @@ exports.shouldCorrectlyDropTheDatabaseWithGenerators = {
       // Let's drop the database
       yield db.dropDatabase();
 
-      // Wait to seconds to let it replicate across
+      // Wait two seconds to let it replicate across
       setTimeout(function() {
         co(function*() {
           // Get the admin database

test/functional/operation_promises_example_tests.js

@@ -3271,7 +3271,7 @@ exports.shouldCorrectlyDropTheDatabaseWithPromises = {
         // Let's drop the database
         db.dropDatabase().then(function(result) {
 
-          // Wait to seconds to let it replicate across
+          // Wait two seconds to let it replicate across
           setTimeout(function() {
             // Get the admin database
             db.admin().listDatabases().then(function(dbs) {