Update how-to-marshal-callbacks-and-delegates-by-using-cpp-interop.md

typo: underlaying -> underlying

Author: Veverke

docs/dotnet/how-to-marshal-callbacks-and-delegates-by-using-cpp-interop.md

@@ -18,7 +18,7 @@ The following example demonstrates how to configure an unmanaged API to trigger
 
 Notice that is it possible, but not necessary, to pin the delegate using [pin_ptr (C++/CLI)](../extensions/pin-ptr-cpp-cli.md) to prevent it from being re-located or disposed of by the garbage collector. Protection from premature garbage collection is needed, but pinning provides more protection than is necessary, as it prevents collection but also prevents relocation.
 
-If a delegate is re-located by a garbage collection, it will not affect the underlaying managed callback, so <xref:System.Runtime.InteropServices.GCHandle.Alloc%2A> is used to add a reference to the delegate, allowing relocation of the delegate, but preventing disposal. Using GCHandle instead of pin_ptr reduces fragmentation potential of the managed heap.
+If a delegate is re-located by a garbage collection, it will not affect the underlying managed callback, so <xref:System.Runtime.InteropServices.GCHandle.Alloc%2A> is used to add a reference to the delegate, allowing relocation of the delegate, but preventing disposal. Using GCHandle instead of pin_ptr reduces fragmentation potential of the managed heap.
 
 ```cpp
 // MarshalDelegate1.cpp