Use 'parameter' high-light group

To align with neovim's usage, use `parameter` instead of
`variable.parameter`.

queries/highlights.scm

@@ -94,7 +94,7 @@
   name: (identifier) @method)
 
 (parameters
-  name: (identifier) @variable.parameter)
+  name: (identifier) @parameter)
 ; }}}
 
 ; Declarations {{{