Fixed parameter name in README

Actually it's 'stackIndex', not 'stackingIndex'.
Merge pull request #34 from esn303/patch-1

Fixed parameter name in README
Updated to v1.2.5

Updated plugin to v1.2.5, mostly involved fixing timing issues. Instead
of relying on the transitionend event that lacks cross-browser
compatibility and standardisation, I have chosen to fall back to JS’
native setTimeout and clearTimeout functions.
Updated minified JS
Merge branch 'master' into gh-pages

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