Fixing a broken link in the Index to properly link to the section below for Force.com

free-programming-books.md

@@ -47,7 +47,7 @@
 * [Erlang](#erlang)
 * [Flex](#flex)
 * [F#](#f-sharp)
-* [Force.com](#salesforce)
+* [Force.com](#forcecom)
 * [Forth](#forth)
 * [Git](#git)
 * [Go](#go)