Correct typo within introduction-1.3.1.js

Effect is a noun, not a verb.
Affect can either be a noun or a verb. In our case, 'affect' is the
appropriate verb for the spec's description.

Further reference:
http://www.etymonline.com/index.php?term=effect
http://www.etymonline.com/index.php?term=affect
Merge pull request #470 from mizuhands/gh-pages

Correct typo within introduction-1.3.1.js