After update to Drush 7 still version 6
The problem is that the old version of Drush is still in your $PATH, and comes before the new version.

The Drush installation instructions says:

Now add Drush to your system path by placing export PATH="$HOME/.composer/vendor/bin:$PATH" into your ~/.bash_profile (Mac OS users) or into your ~/.bashrc (Linux users).

What it does not mention is that changes to your .bashrc file are not immediately reflected in your running system.  You need do one of:


Restart.
Close and re-open all of your terminal windows.
Type source ~/.bashrc in all of your open terminal windows.


(Listed in order from easiest and most disruptive, to more work but less disruptive.)  Substitute .bash_profile in place of .bashrc if you made your modification there.