update version of winreg to 0.51.0

Update the version of winreg to latest, which eliminates the build dependency on winapi.

cargo test -q results:

running 5 tests
.....
test result: ok. 5 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.05s

cargo tree output diff:

$ diff ../before.txt ../after.txt
25c25
< └── winreg v0.11.0
---
> └── winreg v0.51.0
27c27,29
<     └── winapi v0.3.9
---
>     └── windows-sys v0.48.0
>         └── windows-targets v0.48.5
>             └── windows_x86_64_msvc v0.48.5

Further tested by updating build.rs for tray-item's examples/windows app to use embed_resource::compile(...) and verified that the example app properly built with icon embedding.

nabijaczleweli / rust-embed-resource

update version of winreg to 0.51.0 #61