Fix 'method' keyword high-lighting

It makes more sense to add it to `keyword.function`, neovim does not
have a `keyword.method` category, and `method` is for the method name
itself.

queries/highlights.scm

@@ -16,6 +16,7 @@
 ; Keywords {{{
 [
  "function"
+ "method"
  "primitive"
 ] @keyword.function
 
@@ -30,9 +31,6 @@
  "new"
 ] @keyword.constructor
 
-[
- "method"
-] @keyword.method
 
 [
   "import"

test/highlight/object-oriented.tig

@@ -12,7 +12,7 @@ let
     var a := 12
 
     method meth() : int = self.a
-    /* <- keyword.method */
+    /* <- keyword.function */
     /*     ^ method */
     /*                    ^ variable.builtin */
   }