Update books

ehuss · ehuss · commit 2af3b20ad8f3 · 2021-08-23T19:42:31.000-07:00
diff --git a/src/doc/book b/src/doc/book
@@ -1 +1 @@
-Subproject commit 7e49659102f0977d9142190e1ba23345c0f00eb1
+Subproject commit 687e21bde2ea10c261f79fa14797c5137425098d
diff --git a/src/doc/reference b/src/doc/reference
@@ -1 +1 @@
-Subproject commit 4884fe45c14f8b22121760fb117181bb4da8dfe0
+Subproject commit da6ea9b03f74cae0a292f40315723d7a3a973637
diff --git a/src/doc/rust-by-example b/src/doc/rust-by-example
@@ -1 +1 @@
-Subproject commit 0dc9cd4e89f00cb5230f120e1a083916386e422b
+Subproject commit 04f489c889235fe3b6dfe678ae5410d07deda958
diff --git a/src/doc/rustc-dev-guide b/src/doc/rustc-dev-guide
@@ -1 +1 @@
-Subproject commit c4644b427cbdaafc7a87be0ccdf5d8aaa07ac35f
+Subproject commit cf0e151b7925a40f13fbc6573c6f97d5f94c7c17
