Update book.toml rename author field to authors

Author: szabgab

book.toml

@@ -1,7 +1,7 @@
 [book]
 title = "Rust By Example"
 description = "Rust by Example (RBE) is a collection of runnable examples that illustrate various Rust concepts and standard libraries."
-author = "The Rust Community"
+authors = ["The Rust Community"]
 
 [output.html.playpen]
 editable = true