Requires once_cell 1.14

[Hinton]

#1395 started using Lazy:.get_mut which requires version 1.14 or newer of once_cell. The requirement in napi/cargo.toml has a loose requirement on version 1. This caused a compilation error on my environment when upgrading napi.

I believe the solution would be to change the dependency version to ^1.14which should ensure it gets compiled with a compatible version of the dependency.

Full error I get when compiling with an older version of once_cell:

  --> .cargo\registry\src\github.com-1ecc6299db9ec823\napi-2.10.3\src\tokio_runtime.rs:23:29
   |
23 |     if let Some(rt) = Lazy::get_mut(unsafe { &mut RT }) {
   |                             ^^^^^^^ function or associated item not found in `once_cell::sync::Lazy<_, _>`