Fixing typo in prelude documentation

Author: mechaxl

src/libstd/prelude/mod.rs

@@ -45,7 +45,7 @@
 //!
 //! The difference between 'the prelude' and these other preludes is that they
 //! are not automatically `use`'d, and must be imported manually. This is still
-//! easier than importing all of their consitutent components.
+//! easier than importing all of their constituent components.
 //!
 //! # Prelude contents
 //!