Mark myself as inactive

Due to legal reasons, I no longer can be affiliated with the youtube-dl project.

about.html

@@ -30,7 +30,7 @@
 
 <ul>
 <li><a href="https://github.com/rg3">Ricardo Garcia Gonzalez</a>: original author, program core.</li>
-<li><a href="https://github.com/phihag">Philipp Hagemeister</a>: core developer, maintainer since 2011.</li>
+<li><a href="https://github.com/phihag">Philipp Hagemeister</a>: core developer, maintainer 2011-2016.</li>
 <li><a href="https://github.com/FiloSottile">Filippo Valsorda</a>: core developer, Windows build, testing.</li>
 <li><a href="https://github.com/jaimeMF">Jaime Marquínez Ferrándiz</a>: core developer.</li>
 <li><a href="https://github.com/naglis">Naglis Jonaitis</a>: core developer.</li>