Capitalize safety comments

Author: Flying-Toast

alloc/src/alloc.rs

@@ -157,7 +157,7 @@ impl Global {
         }
     }
 
-    // Safety: Same as `AllocRef::grow`
+    // SAFETY: Same as `AllocRef::grow`
     #[inline]
     unsafe fn grow_impl(
         &mut self,

alloc/src/collections/vec_deque.rs

@@ -2392,7 +2392,7 @@ impl<T> VecDeque<T> {
         }
     }
 
-    // Safety: the following two methods require that the rotation amount
+    // SAFETY: the following two methods require that the rotation amount
     // be less than half the length of the deque.
     //
     // `wrap_copy` requires that `min(x, cap() - x) + copy_len <= cap()`,