Fix the definitions of 'reference' and 'pointer' in string_view that no one uses :-). Thanks to K-ballo for the catch.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@321188 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/string_view b/include/string_view
index 4d83582..72cf816 100644
--- a/include/string_view
+++ b/include/string_view
@@ -196,9 +196,9 @@
     // types
     typedef _Traits                                    traits_type;
     typedef _CharT                                     value_type;
-    typedef const _CharT*                              pointer;
+    typedef _CharT*                                    pointer;
     typedef const _CharT*                              const_pointer;
-    typedef const _CharT&                              reference;
+    typedef _CharT&                                    reference;
     typedef const _CharT&                              const_reference;
     typedef const_pointer                              const_iterator; // See [string.view.iterators]
     typedef const_iterator                             iterator;