vim: add 'move' to rustStorage
auto merge of #18789 : cuviper/rust/vim-move, r=alexcrichton

It used to be in `rustKeyword`, but commit 5c75f210ba6e450fb1603b50ca0a4805f13173d7 removed it.  It was reintroduced as a keyword in 0.12.0 to indicate by-value closures, and I think `rustStorage` highlighting makes sense for that purpose.