feat(colors): provide defaults for `nvim-compe`

`nvim-compe` does not use the `FloatBorder` highlight group as defined
by the API. Instead, it uses the default `NormalFloat` group. To
normalize the look of `nvim-compe` with every other float we're adding this
default.

colors/highlite.lua

@@ -894,6 +894,9 @@ local highlight_groups = {
 	GitSignsAdd = 'GitGutterAdd',
 	GitSignsChange = 'GitGutterChange',
 	GitSignsDelete = 'GitGutterDelete',
+
+	--[[ 4.4.16. nvim-compe ]]
+	CompeDocumentationBorder = 'FloatBorder',
 }
 
 --[[ Step 5: Terminal Colors