replace util interpolation with shipwright

lua/zenbones/util.lua

@@ -1,12 +1,5 @@
 local M = {}
 
--- got from http://lua-users.org/wiki/StringInterpolation
-function M.interp(s, tab)
-	return (s:gsub("($%b{})", function(w)
-		return tab[w:sub(3, -2)] or w
-	end))
-end
-
 function M.apply_colorscheme()
 	local colors_name = vim.api.nvim_get_var "colors_name"
 	package.loaded[colors_name] = nil