Update links to WASI docs in time.rs module

Since the docs for the WASI API are now evolving in [WebAssembly/WASI] repo,
I thought it might be useful to update the links in the docs to point to that location
instead of using the outdated `CraneStation/wasmtime` destination.

[WebAssembly/WASI]: https://github.com/WebAssembly/WASI

src/libstd/time.rs

@@ -76,7 +76,7 @@ pub use core::time::Duration;
 /// [QueryPerformanceCounter]: https://docs.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounter
 /// [`insecure_time` usercall]: https://edp.fortanix.com/docs/api/fortanix_sgx_abi/struct.Usercalls.html#method.insecure_time
 /// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
-/// [__wasi_clock_time_get (Monotonic Clock)]: https://github.com/CraneStation/wasmtime/blob/master/docs/WASI-api.md#clock_time_get
+/// [__wasi_clock_time_get (Monotonic Clock)]: https://github.com/WebAssembly/WASI/blob/master/phases/snapshot/docs.md#clock_time_get
 /// [clock_gettime (Monotonic Clock)]: https://linux.die.net/man/3/clock_gettime
 /// [mach_absolute_time]: https://developer.apple.com/library/archive/documentation/Darwin/Conceptual/KernelProgramming/services/services.html
 /// [clock_time_get (Monotonic Clock)]: https://nuxi.nl/cloudabi/#clock_time_get
@@ -157,7 +157,7 @@ pub struct Instant(time::Instant);
 /// [timekeeping in SGX]: https://edp.fortanix.com/docs/concepts/rust-std/#codestdtimecode
 /// [gettimeofday]: http://man7.org/linux/man-pages/man2/gettimeofday.2.html
 /// [clock_gettime (Realtime Clock)]: https://linux.die.net/man/3/clock_gettime
-/// [__wasi_clock_time_get (Realtime Clock)]: https://github.com/CraneStation/wasmtime/blob/master/docs/WASI-api.md#clock_time_get
+/// [__wasi_clock_time_get (Realtime Clock)]: https://github.com/WebAssembly/WASI/blob/master/phases/snapshot/docs.md#clock_time_get
 /// [GetSystemTimeAsFileTime]: https://docs.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimeasfiletime
 ///
 /// **Disclaimer:** These system calls might change over time.