Update composer.json

target-dir is not needed. All it does, is nest everything another level deeper. It should only be used for completing psr-0 paths.

composer.json

@@ -5,6 +5,5 @@
   , "homepage": "http://twitter.github.com/bootstrap/"
   , "author": "Twitter Inc."
   , "license": "Apache-2.0"
-  , "target-dir": "twitter/bootstrap"
 
 }