Update free-programming-books.md

Fixed typo.
Merge pull request #795 from guillaume-nargeot/master

[en] Added CS240h: Functional Systems in Haskell
Modified the Django list to contain version numbers
Merge pull request #796 from Kentoseth/master

Modified the Django list to contain version numbers
Fix the URL for the Introduction to Data Science book
Merge pull request #797 from ryanoreilly/master

Fix the URL for the Introduction to Data Science book
Update Windows 8 book; adding a incomplete v2
Merge pull request #798 from KilFer/patch-1

Update Windows 8 book; adding a incomplete v2
20,000
Add a bash book:  Conquering the Command Line
[es] New section (& book): Erlang
Merge pull request #799 from HungMingWu/master

Add a bash book:  Conquering the Command Line
Merge pull request #800 from esparta/master

[es] New section (& book): Erlang
Adding Code Guide to HTML/CSS section.
Merge pull request #801 from jbranchaud/adding-html-css-resource

Adding Code Guide to HTML/CSS section.
Add a single haskell book
Merge pull request #802 from vikt0rs/master

Add one more book about haskell
[es] Adding Erlang book
Merge pull request #803 from esparta/master

[es] Adding Erlang book
Add C book "Using C on the UNIX System"

By David A. Curry. Made available for personal use by the author.