allow files to be opened and checked outside of project directory

Author: jlevesy

syntax_checkers/rust/cargo.vim

@@ -46,6 +46,7 @@ endfunction
 
 call g:SyntasticRegistry.CreateAndRegisterChecker({
     \ 'filetype': 'rust',
+    \ 'cwd': expand('%:p:h'),
     \ 'name': 'cargo'})
 
 let &cpo = s:save_cpo