reduce spacing in awesome fonts iconset

This replaces the previous normal spacing character (which is the
usual ASCII 0x20 SPACE) by a *narrower* spacer (which is unicode
U+2009 THIN SPACE).

I found that space thanks to

https://en.wikipedia.org/wiki/Space_(punctuation)#Types_of_spaces

... and specifically:

https://en.wikipedia.org/wiki/Thin_space

... and this actually works, amazingly. Probably because it is pretty
standard as it's part of the SI specification (thousands separator),
Tex (`\thinspace` or `\,`), and HTML (` `)

Closes: #888

themes/icons/awesome-fonts.json

@@ -1,7 +1,7 @@
 {
   "defaults": {
     "separator": "",
-    "padding": " ",
+    "padding": " ",
     "unknown": {
       "prefix": ""
     },