update bson version in readme (#229)

Yarn · kyeah · commit 66f70dc763d9 · 2017-07-24T14:46:10.000-04:00
diff --git a/README.md b/README.md
@@ -22,7 +22,7 @@ The driver is available on crates.io. To use the MongoDB driver in your code, ad
 
 ```
 [dependencies]
-bson = "0.8.0"
+bson = "0.9.0"
 mongodb = "0.3.0"
 ```
 
