minor: bump bson version to 1.2.1

Author: patrickfreed

Cargo.toml

@@ -34,7 +34,7 @@ bson-u2i = ["bson/u2i"]
 async-trait = "0.1.24"
 base64 = "0.11.0"
 bitflags = "1.1.0"
-bson = "1.2.0"
+bson = "1.2.1"
 chrono = "0.4.7"
 derivative = "2.1.1"
 err-derive = "0.2.3"