Wrap symbol-start and symbol-end for not highlighting like true_false

Author: syohex

elixir-mode.el

@@ -367,7 +367,9 @@ is used to limit the scan."
      1 font-lock-type-face)
 
     ;; Atoms and singleton-like words like true/false/nil.
-    (,(elixir-rx (group (or atoms "true" "false" "nil"))
+    (,(elixir-rx symbol-start
+                 (group (or atoms "true" "false" "nil"))
+                 symbol-end
                  (zero-or-more space)
                  (optional "="))
      1 elixir-atom-face)

test/elixir-mode-font-test.el

@@ -248,7 +248,7 @@ some_expr"
    (should (eq (elixir-test-face-at 2) 'font-lock-variable-name-face))
    (should (eq (elixir-test-face-at 4) 'font-lock-variable-name-face))))
 
-(ert-deftest elixir-mode-syntax-table/fontify-assignment-with-special-atom ()
+(ert-deftest elixir-mode-syntax-table/fontify-assignment-with-singleton ()
   "https://github.com/elixir-lang/emacs-elixir/issues/245"
   :tags '(fontification syntax-table)
   (elixir-test-with-temp-buffer