internal/unsafeheader: fix typos in comments

The typos in the package godoc comment were pointed out in CL 231223
which added similar functionality to the main Go repository. Also
correct the name in the godoc comment for type String.

Change-Id: I69910f3e24b1222190e1adf7fc3d425f0006f96e
Reviewed-on: https://go-review.googlesource.com/c/sys/+/231517
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
diff --git a/internal/unsafeheader/unsafeheader.go b/internal/unsafeheader/unsafeheader.go
index bfc5d3c..e07899b 100644
--- a/internal/unsafeheader/unsafeheader.go
+++ b/internal/unsafeheader/unsafeheader.go
@@ -3,10 +3,10 @@
 // license that can be found in the LICENSE file.
 
 // Package unsafeheader contains header declarations for the Go runtime's
-// slice and struct implementations.
+// slice and string implementations.
 //
 // This package allows x/sys to use types equivalent to
-// reflect.SliceHeader and reflect.StructHeader without introducing
+// reflect.SliceHeader and reflect.StringHeader without introducing
 // a dependency on the (relatively heavy) "reflect" package.
 package unsafeheader
 
@@ -22,7 +22,7 @@
 	Cap  int
 }
 
-// StringHeader is the runtime representation of a string.
+// String is the runtime representation of a string.
 // It cannot be used safely or portably and its representation may change in a later release.
 type String struct {
 	Data unsafe.Pointer