fix typo in internal comment

Author: the8472

src/bootstrap/builder.rs

@@ -1491,7 +1491,7 @@ impl<'a> Builder<'a> {
 
         // Add extra cfg not defined in/by rustc
         //
-        // Note: Altrough it would seems that "-Zunstable-options" to `rustflags` is useless as
+        // Note: Although it would seems that "-Zunstable-options" to `rustflags` is useless as
         // cargo would implicitly add it, it was discover that sometimes bootstrap only use
         // `rustflags` without `cargo` making it required.
         rustflags.arg("-Zunstable-options");