Fix spelling in documents (#6948)

* Update roxygen2 doc.

Co-authored-by: fis <jm.yuan@outlook.com>

rabit/include/rabit/internal/rabit-inl.h

@@ -102,7 +102,7 @@ inline void Reducer(const void *src_, void *dst_, int len, const MPI::Datatype &
 }
 }  // namespace op
 
-// intialize the rabit engine
+// initialize the rabit engine
 inline bool Init(int argc, char *argv[]) {
   return engine::Init(argc, argv);
 }

rabit/include/rabit/internal/socket.h

@@ -615,7 +615,7 @@ struct PollHelper {
   }
 
   /*!
-   * \brief peform poll on the set defined, read, write, exception
+   * \brief perform poll on the set defined, read, write, exception
    * \param timeout specify timeout in milliseconds(ms) if negative, means poll will block
    * \return
    */