Update spin.js

I'm not sure what this line was doing, but it was setting the position of my element to 0,0 which was in the upper left corner.  I had nothing in my div so maybe the height wasn't work properly?  50% on each centered the spinner div in my div.
fix as suggested by @jamesandres: https://github.com/skilesare/spin.js/commit/f1550c120a83e8061bbf883029da482359a3dd50
Merge branch 'skilesare-50pct-on-empty-div-pos' into gh-pages
gitignore editor bak files