Fix Windows hyperlinks for paths with spaces

Fixes #1843

Changed the host() function for Windows to return '/' instead of ''
to generate RFC 3986 compliant file URLs with three slashes.

Before: file://C:/test/hi%20there.txt (broken)
After:  file:///C:/test/hi%20there.txt (works)

This fixes hyperlinks failing on Windows when file paths contain
spaces or other characters that require percent-encoding.

src/hyperlink.rs

@@ -58,7 +58,7 @@ fn host() -> &'static str {
 
 #[cfg(not(unix))]
 const fn host() -> &'static str {
-    ""
+    "/"
 }
 
 #[cfg(test)]