https

README.md

@@ -69,7 +69,7 @@ for example:
 - ...
 
 
-[<img src="http://i.imgur.com/yYw46aF.jpg" align="right" alt="The book Dynamic Documents with R and knitr" />](http://amzn.com/1498716962)
+[<img src="http://i.imgur.com/yYw46aF.jpg" align="right" alt="The book Dynamic Documents with R and knitr" />](https://amzn.com/1498716962)
 
 The package **knitr** was designed to give the user access to every part of
 the process of dealing with a literate programming document, so there is no
@@ -93,7 +93,7 @@ reasonable default settings. A few manuals are available such as the [main
 manual](https://yihui.name/knitr/demo/manual/), and the
 [graphics
 manual](https://yihui.name/knitr/demo/graphics/). For a
-more organized reference, see the [knitr book](http://amzn.com/1498716962).
+more organized reference, see the [knitr book](https://amzn.com/1498716962).
 
 ## License