misc/notepadplus: fix some number syntax highlight issue

notepadplus can only support some normal golang's hex and imaginary numbers.
it can't detect some special number, eg. 1./1.e/1.i/1+0.1i (omit "0" in ".0").

R=golang-dev, gvdschoot
CC=ajstarks, golang-dev
https://codereview.appspot.com/13401047

Committer: Andrew Gerrand <adg@golang.org>