Use github upstream for Ltk.

quicklisp · quicklisp · commit dc49d5973658 · 2019-01-05T07:50:03.000-05:00
diff --git a/projects/ltk/source.txt b/projects/ltk/source.txt
@@ -1 +1,2 @@
-http http://www.peter-herth.de/ltk/ltk-0.981.tgz
+git https://github.com/herth/ltk.git
+

Original file line number	Diff line number	Diff line change
`@@ -1 +1,2 @@`
`1`		`-http http://www.peter-herth.de/ltk/ltk-0.981.tgz`
	`1`	`+git https://github.com/herth/ltk.git`
	`2`	`+`