use special.string.symbol instead of symbol

this aligns better with how ruby highlights symbols

book/src/themes.md

@@ -119,8 +119,7 @@ We use a similar set of scopes as
   - `special`
     - `path`
     - `url`
-
-- `symbol` - Elixir atoms, Ruby symbols, Clojure keywords
+    - `symbol` - Erlang/Elixir atoms, Ruby symbols, Clojure keywords
 
 - `comment` - Code comments
   - `line` - Single line comments (`//`)

runtime/queries/elixir/highlights.scm

@@ -97,7 +97,7 @@
   (quoted_atom)
   (keyword)
   (quoted_keyword)
-] @symbol
+] @string.special.symbol
 
 [
   (string)