minor: update crate description (#198)

Author: saghm

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 authors = ["Saghm Rossi <[email protected]>", "Patrick Freed <[email protected]>"]
-description = "The official MongoDB driver for Rust (currently in alpha)"
+description = "The official MongoDB driver for Rust"
 edition = "2018"
 documentation = "https://docs.rs/mongodb"
 keywords = ["mongo", "mongodb", "database", "bson", "nosql"]