Add fish shell support

[ltgouvea]

When I try to analyze files using fish as my default shell I get this error message. I'm no shell redirection master but I'm willing to contribute on a solution for this. Maybe we could force this command to be executed using something like sh -c

fish: Expected a command, but instead found a '&'
phpstan analyse --no-progress -l2 . |& /home/lgouvea/.vim/plugged/vim-phpstan/plugin/phpstan_filter 2>&1| tee /tmp/vvRTJoL/7