Don't quote nil and t in doc strings

This is as per "Tips for Documentation Strings" in the elisp manual.
For consistency, do the same in diagnostics and comments.

1 files changed, 1 insertions, 1 deletions

diff --git a/lisp/widget.el b/lisp/widget.el
index 539f91e63a0..d62f7ffd8d1 100644
--- a/lisp/widget.el
+++ b/lisp/widget.el
@@ -85,7 +85,7 @@ create identical widgets:
 The third argument DOC is a documentation string for the widget."
   ;;
   (unless (or (null doc) (stringp doc))
-    (error "widget documentation must be `nil' or a string."))
+    (error "widget documentation must be nil or a string."))
   (put name 'widget-type (cons class args))
   (put name 'widget-documentation (purecopy doc))
   name)