* core/core-configuration-layer.el: Fix bug on configuration-layer/describe-package

[sunlin7]

Fix a bug when revert the buffer on configuration-layer/describe-package buffer.
Reproduce steps:
0. Start Spacemacs,

1. Pressing SPC h d P and input a package name to show a help buffer for a package;
2. Pressing SPC b R to revert the buffer, will trigger an error, like

Debugger entered--Lisp error: (void-function nil)
  nil()
  apply(nil nil)
  help-mode-revert-buffer(t nil)
  revert-buffer(t)
  funcall-interactively(revert-buffer t)
  call-interactively(revert-buffer nil nil)
  command-execute(revert-buffer)

[bcc32]

Nice, thanks. I reworded the commit to be slightly more specific about the bug, but otherwise merged as-is.

[sunlin7]

Thank you !