update readme

Author: garris

README.md

@@ -3,7 +3,7 @@
 
 BackstopJS automates CSS regression tesing of your responsive web UI by comparing DOM screenshots at various viewport sizes.
 
-**Try the step-by-step tutorial on [http://css-tricks.com/automating-css-regression-testing/](http://css-tricks.com/automating-css-regression-testing/).**
+**Try the step-by-step tutorial on [css-tricks.com](http://css-tricks.com/automating-css-regression-testing/).**
 
 Learn more at [http://BackstopJS.org/](http://garris.github.io/BackstopJS/).