Fix wrongly disabled default timestamps feature

Hi!
I have noticed that after commits, which replaces "chrono" dependency with "time", logger does not print timestamps by default.

In this https://github.com/borntyping/rust-simple_logger/blob/main/src/lib.rs#L37 line, "chrono" feature-gate was used before dependency changes. Now it is "timestamps". 
So I just try to actualize default feature gates in project manifest.

Cargo.toml

@@ -8,7 +8,7 @@ repository = "https://github.com/borntyping/rust-simple_logger"
 edition = "2018"
 
 [features]
-default = ["colored", "time"]
+default = ["colored", "timestamps"]
 colors = ["colored"]
 threads = []
 timestamps = ["time"]