fix(modal): enhance modal.open() to calculate
    initial modal y-offset correctly on IE9
fix(modal): eliminate test jshint issues
refactor(modal): Only use pageYOffset to calculate initial position
fix(topbar): Fix position calculation for IE

IE does not define scrollY. It defines pageYOffset which is an alias for
scrollY in other browsers.
Update changelog for 0.5.1
Update upcoming version in package.json
chore(release): v0.5.1 :shipit:
chore(release): Starting v0.6.0-SNAPSHOT
chore(release): 0.5.2