Fix two index links

free-programming-books-ja.md

@@ -40,7 +40,7 @@
 * [Maven](#maven)
 * [Mercurial](#mercurial)
 * [NoSQL](#nosql)
-* [Objective-C](#objective_c)
+* [Objective-C](#objective-c)
 * [OCaml](#ocaml)
 * [Perl](#perl)
 * [PHP](#php)
@@ -57,7 +57,7 @@
 * [Smalltalk](#smalltalk)
 * [SQL(実装非依存)](#sql%e5%ae%9f%e8%a3%85%e9%9d%9e%e4%be%9d%e5%ad%98)
 * [Standard ML](#standard-ml)
-* [Tcl/Tk](#tcl-ftk)
+* [Tcl/Tk](#tcltk)
 * [TypeScript](#typescript)
 * [VBA](#vba)
 * [Vim](#vim)