Include - in operator syntax class

`-` is subtraction in elixir, not part of a symbol.

Author: aaronjensen

elixir-smie.el

@@ -79,6 +79,7 @@
     ;; Note that ?_ might be better as class "_", but either seems to
     ;; work:
     (modify-syntax-entry ?| "." table)
+    (modify-syntax-entry ?- "." table)
     (modify-syntax-entry ?_ "_" table)
     (modify-syntax-entry ?? "w" table)
     (modify-syntax-entry ?~ "w" table)