.gitmodules: use the official Git URL w/o redirect

nodakai · web-flow · commit 1f93a78cdc38 · 2017-04-06T21:48:56.000+08:00
diff --git a/.gitmodules b/.gitmodules
@@ -25,4 +25,4 @@
 	url = https://github.com/rust-lang-nursery/reference.git
 [submodule "book"]
 	path = src/doc/book
-	url = https://github.com/rust-lang/book
+	url = https://github.com/rust-lang/book.git
