(syms_of_buffer) <default-major-mode>: Doc fix.

src/buffer.c

@@ -5500,8 +5500,8 @@ Decimal digits after the % specify field width to which to pad.  */);
 
   DEFVAR_LISP_NOPRO ("default-major-mode", &buffer_defaults.major_mode,
 		     doc: /* *Major mode for new buffers.  Defaults to `fundamental-mode'.
-nil here means use current buffer's major mode, provided it is not
-marked as "special".
+A value of nil means use current buffer's major mode,
+provided it is not marked as "special".
 
 When a mode is used by default, `find-file' switches to it
 before it reads the contents into the buffer and before