swiper.el (swiper--line): Don't replace tabs with spaces

The original intent, I think was the alignment in the minibuffer in
case of mixed tabs and spaces.

But doing that prevents `wgrep' from working correctly for files with
tabs.

Fixes #1468

swiper.el

@@ -339,9 +339,7 @@
 
     (concat
      " "
-     (replace-regexp-in-string
-      "\t" "    "
-      (buffer-substring beg end)))))
+     (buffer-substring beg end))))
 
 (declare-function outline-show-all "outline")