Prefer core::marker and core::mem to fix --no-default-features -F malloc_size_of (#83)

Author: kpcyrd

src/lib.rs

@@ -2138,8 +2138,8 @@ impl<T> MallocShallowSizeOf for ThinVec<T> {
         }
 
         assert_eq!(
-            std::mem::size_of::<Self>(),
-            std::mem::size_of::<*const ()>()
+            core::mem::size_of::<Self>(),
+            core::mem::size_of::<*const ()>()
         );
         unsafe { ops.malloc_size_of(*(self as *const Self as *const *const ())) }
     }