allow files to be opened and checked outside of project directory

Author: jlevesy

syntax_checkers/rust/cargo.vim

@@ -41,6 +41,7 @@ function! SyntaxCheckers_rust_cargo_GetLocList() dict
 
     return SyntasticMake({
         \ 'makeprg': makeprg,
+        \ 'cwd': expand('%:p:h'),
         \ 'errorformat': errorformat })
 endfunction