Fix Appendix G

Author: Jun-ya Norimatsu

second-edition/src/appendix-07-nightly-rust.md

@@ -1,6 +1,6 @@
 <!-- # Appendix G - How Rust is Made and “Nightly Rust” -->
 
-## 付録G: Rustが作られ方と“Nightly Rust”
+## 付録G: Rustの作られ方と“Nightly Rust”
 
 <!-- This appendix is about how Rust is made and how that affects you as a Rust -->
 <!-- developer. We mentioned that the output in this book was generated by stable -->