* packages/num3-mode/num3-mode.el: Fix compilation warnings.

* packages/num3-mode/num3-mode.el: Fix compilation warnings.

Fixes the following warnings:

In toplevel form:
num3-mode.el:47:1:Warning: defcustom for ‘num3-group-size’ fails to specify
    type
num3-mode.el:47:1:Warning: defcustom for ‘num3-group-size’ fails to specify
    type
num3-mode.el:50:1:Warning: defcustom for ‘num3-threshold’ fails to specify
    type
num3-mode.el:50:1:Warning: defcustom for ‘num3-threshold’ fails to specify
    type

In num3-mode:
num3-mode.el:95:11:Warning: ‘font-lock-fontify-buffer’ is for interactive use
    only; use ‘font-lock-ensure’ or ‘font-lock-flush’ instead.