Fix Sphinx build error caused by bad indentation

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@291039 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/DesignDocs/VisibilityMacros.rst b/docs/DesignDocs/VisibilityMacros.rst
index 5eae9a7..37539ec 100644
--- a/docs/DesignDocs/VisibilityMacros.rst
+++ b/docs/DesignDocs/VisibilityMacros.rst
@@ -80,7 +80,7 @@
 
   **GCC Behavior**: GCC ignores visibility attributes applied the type in
   extern template declarations and applying an attribute results in a warning.
-   However since `_LIBCPP_TEMPLATE_VIS` is the same as
+  However since `_LIBCPP_TEMPLATE_VIS` is the same as
   `__attribute__((visibility("default"))` the visibility is already correct.
   The macro has an empty definition with GCC.