Update src/items/functions.md

Co-Authored-By: Mazdak Farrokhzad <[email protected]>

Author: nikomatsakis

src/items/functions.md

@@ -282,7 +282,7 @@ the same.
 
 Unsafe is used on an async function in precisely the same way that it
 is used on other functions: it indicates that the function imposes
-some additional obligations on its caller to ensure safety. As in any
+some additional obligations on its caller to ensure soundness. As in any
 other unsafe function, these conditions may extend beyond the initial
 call itself -- in the snippet above, for example, the `unsafe_example`
 function took a pointer `x` as argument, and then (when awaited)