Script font family not supported in font queries

[corranwebster]

If you do

gc.set_font(Font(family=SCRIPT, size=24))

in a backend that uses kiva.fonttools to find font files, then you get the following error:

/Users/cwebster/.edm/envs/edm/lib/python3.6/site-packages/kiva/fonttools/font_manager.py:294: UserWarning: findfont: Font family ['script'] not found. Falling back to sans-serif
  % (query.get_family(), self.default_family)

This is because script is not listed in the options here:

enable/kiva/fonttools/_constants.py

Lines 11 to 76 in 7079309

	font_family_aliases = {
	"serif",
	"sans-serif",
	"sans serif",
	"cursive",
	"fantasy",
	"monospace",
	"sans",
	"modern",
	}
	preferred_fonts = {
	"fantasy": [
	"Comic Sans MS",
	"Chicago",
	"Charcoal",
	"ImpactWestern",
	"fantasy",
	],
	"cursive": [
	"Apple Chancery",
	"Textile",
	"Zapf Chancery",
	"Sand",
	"cursive",
	],
	"monospace": [
	"Bitstream Vera Sans Mono",
	"DejaVu Sans Mono",
	"Andale Mono",
	"Nimbus Mono L",
	"Courier New",
	"Courier",
	"Fixed",
	"Terminal",
	"monospace",
	],
	"serif": [
	"Bitstream Vera Serif",
	"DejaVu Serif",
	"New Century Schoolbook",
	"Century Schoolbook L",
	"Utopia",
	"ITC Bookman",
	"Bookman",
	"Nimbus Roman No9 L",
	"Times New Roman",
	"Times",
	"Palatino",
	"Charter",
	"serif",
	],
	"sans-serif": [
	"Bitstream Vera Sans",
	"DejaVu Sans",
	"Helvetica Neue",
	"Arial",
	"Verdana",
	"Helvetica",
	"Lucida Grande",
	"Geneva",
	"Lucid",
	"Avant Garde",
	"sans-serif",
	],
	}