Documentation cleanup: escape "::" to eliminate a Doxygen warning

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158620 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/AST/ASTContext.h b/include/clang/AST/ASTContext.h
index cb2f694..6ceed17 100644
--- a/include/clang/AST/ASTContext.h
+++ b/include/clang/AST/ASTContext.h
@@ -1473,7 +1473,7 @@
   /// be used to refer to a given template. For most templates, this
   /// expression is just the template declaration itself. For example,
   /// the template std::vector can be referred to via a variety of
-  /// names---std::vector, ::std::vector, vector (if vector is in
+  /// names---std::vector, \::std::vector, vector (if vector is in
   /// scope), etc.---but all of these names map down to the same
   /// TemplateDecl, which is used to form the canonical template name.
   ///