Fix infinite recursion in sorted_vector_{set|map}::insert(const value_type&)

Fix infinite recursion in sorted_vector_{set|map}::insert(const value_type&)

Summary:
We were calling ourself, which MSVC correctly identified:
```
warning C4717: 'folly::sorted_vector_set<int,`anonymous namespace'::less_invert<int>,std::allocator<int>,void>::insert': recursive on all control paths, function will cause runtime stack overflow
```

Just add an explicit `std::move` in to solve the problem.

Reviewed By: yfeldblum

Differential Revision: D3447922

fbshipit-source-id: 803f79510b3dbfeea32a9629238448f69f5b78dc