Make nix optional

- nix dependency is only directly used for i2c in this crate.

Signed-off-by: Ayush Singh <[email protected]>

Author: Ayush1325

Cargo.toml

@@ -16,7 +16,7 @@ edition = "2018"
 gpio_sysfs = ["sysfs_gpio"]
 gpio_cdev = ["gpio-cdev"]
 async-tokio = ["gpio-cdev/async-tokio", "dep:embedded-hal-async", "tokio/time"]
-i2c = ["i2cdev"]
+i2c = ["i2cdev", "nix"]
 spi = ["spidev"]
 serial = ["serialport", "embedded-hal-nb"]
 
@@ -32,7 +32,7 @@ i2cdev = { version = "0.6.0", optional = true }
 nb = "1"
 serialport = { version = "4.2.0", default-features = false, optional = true }
 spidev = { version = "0.6.0", optional = true }
-nix = "0.27.1"
+nix = { version = "0.27.1", optional = true }
 tokio = { version = "1", default-features = false, optional = true }
 
 [dev-dependencies]