Cargo.toml: more semver for avr_delay

In an attempt to publish it. Current error:
| $ AVR_CPU_FREQUENCY_HZ=8_000_000 cargo +nightly publish --target ./avr-atmega328p.json -Z build-std=core
|     Updating crates.io index
|    Packaging ruduino v0.4.0 (/home/gs0604/src/rust/RustAVR/ruduino)
| error: failed to prepare local package for uploading
|
| Caused by:
|   failed to select a version for the requirement `avr_delay = "^0.4"`
|   candidate versions found which didn't match: 0.3.2, 0.3.1, 0.3.0, ...
|   location searched: crates.io index
|   required by package `ruduino v0.4.0 (/home/gs0604/src/rust/RustAVR/ruduino)`

Author: stappersg

Cargo.toml

@@ -29,7 +29,7 @@ all-mcus = []
 
 [dependencies]
 avr-config = { version = "2.0", features = ["cpu-frequency"] }
-avr_delay = { git = "https://github.com/avr-rust/delay", version = "0.4" }
+avr_delay = { git = "https://github.com/avr-rust/delay", version = "0.4.0" }
 avr-std-stub = { version = "1.0", optional = true }
 const_env--value = "0.1"
 target-cpu-macro = "0.1"