Rollup merge of rust-lang#48404 - steveklabnik:second-edition-is-the-best-edition, r=QuietMisdreavus

Manishearth · web-flow · commit 9901befe06c7 · 2018-02-24T15:52:10.000-08:00
Update the book to promote second edition This updates the book repository, but mostly to include rust-lang/book#1180 TL;DR: the second edition is close enough to done that we should universally recommend it over the first edition.
diff --git a/src/doc/book b/src/doc/book
@@ -1 +1 @@
-Subproject commit ec5660820dea91df470dab0b9eb26ef798f20889
+Subproject commit 98921e9de849acdaeaed08cfad6758bb89769b7d
