Update 13.md

correcion of image's url
Merge pull request #32 from MannyDev/patch-4

Update 13.md
Merge pull request #33 from andyque/master

remove cocos2d namespace prefix
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Merge branch 'master' of github.com:chukong/programmers-guide
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resize
Update 2.md

fixing typo and improve readability.
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Merge pull request #37 from kr15to/patch-10

Update 2.md
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typo fix
typo on grammer