Remove mention of rake preview for theme README.
Remove mention of rake preview for theme README.

getandpost/jekyll.github.io,x-way/jekyll,gencer/jekyll,Strangehill/jekyll,Strangehill/jekyll,chrisfinazzo/jekyll,pmarsceill/jekyll,tomjohnson1492/jekyll,getandpost/jekyll.github.io,tomjohnson1492/jekyll,tillgrallert/jekyll,xcatliu/jekyllcn,Strangehill/jekyll,xiebinhqy/jklly_china,jaybe-jekyll/jekyll,fulldecent/jekyll,alex-kovac/jekyll,tillgrallert/jekyll,rlugojr/jekyll,alfredxing/jekyll,x-way/jekyll,xcatliu/jekyllcn,darwin/jekyll,darwin/jekyll,fulldecent/jekyll,xiebinhqy/jklly_china,jeffkole/jekyll,chrisfinazzo/jekyll,rlugojr/jekyll,tillgrallert/jekyll,pmarsceill/jekyll,darwin/jekyll,ZDroid/jekyll,jekyll/jekyll,jekyll/jekyll,jeffkole/jekyll,yhironaka/yhironaka.github.io,gencer/jekyll,alfredxing/jekyll,chrisfinazzo/jekyll,jaybe-jekyll/jekyll,getandpost/jekyll.github.io,noikiy/jekyll,rasa2011/rasa2011.github.io,gencer/jekyll,alex-kovac/jekyll,fulldecent/jekyll,Strangehill/jekyll,tomjohnson1492/jekyll,rlugojr/jekyll,noikiy/jekyll,gencer/jekyll,tomjohnson1492/jekyll,x-way/jekyll,chrisfinazzo/jekyll,ryanshaw/jekyll,jeffkole/jekyll,alex-kovac/jekyll,xiebinhqy/jklly_china,jekyll/jekyll,Strangehill/jekyll,x-way/jekyll,rlugojr/jekyll,alfredxing/jekyll,ZDroid/jekyll,rasa2011/rasa2011.github.io,jaybe-jekyll/jekyll,xcatliu/jekyllcn,alex-kovac/jekyll,ryanshaw/jekyll,noikiy/jekyll,tillgrallert/jekyll,gencer/jekyll,jaybe-jekyll/jekyll,noikiy/jekyll,xiebinhqy/jklly_china,tomjohnson1492/jekyll,ryanshaw/jekyll,darwin/jekyll,ryanshaw/jekyll,jeffkole/jekyll,alex-kovac/jekyll,fulldecent/jekyll,xcatliu/jekyllcn,alfredxing/jekyll,tillgrallert/jekyll,rasa2011/rasa2011.github.io,jekyll/jekyll,pmarsceill/jekyll,pmarsceill/jekyll,ZDroid/jekyll