Incorrect use of `deprecated` attribute

[estebank]

rust-lang/rust#56896 is making the correct use of deprecated mandatory in rustc. We can't apply this as a hard error due to the following use in gcode:

[INFO] [stderr]     Checking gcode v0.3.1 (/opt/crater/workdir)
[INFO] [stderr] error: expected meta item sequence
[INFO] [stderr]   --> src/types.rs:53:5
[INFO] [stderr]    |
[INFO] [stderr] 53 |     #[deprecated = "You probably want the `Gcode::major_number()` and `Gcode::minor_number()` methods instead"]
[INFO] [stderr]    |     ^^--------------------------------------------------------------------------------------------------------^
[INFO] [stderr]    |       |
[INFO] [stderr]    |       help: use the `note` key: `deprecated(note = "You probably want the `Gcode::major_number()` and `Gcode::minor_number()` methods instead")`
[INFO] [stderr] 
[INFO] [stderr] error: expected meta item sequence
[INFO] [stderr]   --> src/types.rs:53:5
[INFO] [stderr]    |
[INFO] [stderr] 53 |     #[deprecated = "You probably want the `Gcode::major_number()` and `Gcode::minor_number()` methods instead"]
[INFO] [stderr]    |     ^^--------------------------------------------------------------------------------------------------------^
[INFO] [stderr]    |       |
[INFO] [stderr]    |       help: use the `note` key: `deprecated(note = "You probably want the `Gcode::major_number()` and `Gcode::minor_number()` methods instead")`

[Michael-F-Bryan]

Thanks for the issue @estebank. I've created a side branch with the fix, and made a new release on crates.io.