fix typo on README.md Psr0Fixer -> psr0
minor #382 fix typo on README.md Psr0Fixer -> psr0 (cordoval)

This PR was squashed before being merged into the 0.5.x-dev branch (closes #382).

Discussion
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fix typo on README.md Psr0Fixer -> psr0

|Q            |A  |
|---          |---|
|Bug Fix?     |n  |
|New Feature? |n  |
|BC Breaks?   |n  |
|Deprecations?|n  |
|Tests Pass?  |y  |
|Fixed Tickets|   |
|License      |MIT|
|Doc PR       |   |

Commits
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363594d fix typo on README.md Psr0Fixer -> psr0