updated history and travis build file

Author: christkv

.travis.yml

@@ -3,6 +3,7 @@ node_js:
   - "0.10"
   - "0.12"
   - "iojs"
+  - "4.0"
 sudo: false
 env:
   - MONGODB_VERSION=2.2.x

HISTORY.md

@@ -5,6 +5,7 @@
 * NOT providing replSet name in MongoClient connection URI will force single server connection. Fixes issue where it was impossible to directly connect to a replicaset member server.
 * Updated mongodb-core to 1.2.12.
 * NODE-541 Initial Support "read committed" isolation level where "committed" means confimed by the voting majority of a replica set.
+* GridStore doesn't share readPreference setting from connection string.
 
 2.0.42 08-18-2015
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