Fix coercin -> coercion typo

src/librustc_typeck/check/coercion.rs

@@ -196,7 +196,7 @@ fn coerce<'a, E, I>(&self, exprs: &E, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<
                 // Function items are coercible to any closure
                 // type; function pointers are not (that would
                 // require double indirection).
-                // Additionally, we permit coercin of function
+                // Additionally, we permit coercion of function
                 // items to drop the unsafe qualifier.
                 self.coerce_from_fn_item(a, a_f, b)
             }