Fix Project-Specific Implementation example

In reference to mailing list conversation: https://groups.google.com/d/msg/php-fig/SJTL1ec46II/3DpYEzJ6Gz8J

 * Ensure namespace prefix has a trailing `\` to ensure incorrect matches do not happen.
   (avoids `Foo\Bar` matching class `Foo\BarBaz`)
 * Removed unneeded `return` statements.