Fix spelling errors in documentation.

src/librustc/middle/infer/higher_ranked/mod.rs

@@ -461,7 +461,7 @@ impl<'a,'tcx> InferCtxtExt for InferCtxt<'a,'tcx> {
 
 /// Constructs and returns a substitution that, for a given type
 /// scheme parameterized by `generics`, will replace every generic
-/// parmeter in the type with a skolemized type/region (which one can
+/// parameter in the type with a skolemized type/region (which one can
 /// think of as a "fresh constant", except at the type/region level of
 /// reasoning).
 ///

src/librustc/middle/ty.rs

@@ -1908,7 +1908,7 @@ pub enum Predicate<'tcx> {
 }
 
 impl<'tcx> Predicate<'tcx> {
-    /// Performs a substituion suitable for going from a
+    /// Performs a substitution suitable for going from a
     /// poly-trait-ref to supertraits that must hold if that
     /// poly-trait-ref holds. This is slightly different from a normal
     /// substitution in terms of what happens with bound regions.  See