Support Fish Shell

[nathf]

When sourcing autovenv.sh I get the following error:

$ source /usr/local/bin/autovenv.sh                                                                   
Unsupported use of '&&'. In fish, please use 'COMMAND; and COMMAND'.
/usr/local/bin/autovenv.sh (line 8):     builtin cd "$@" && do_autovenv
                                                          ^
from sourcing file /usr/local/bin/autovenv.sh
	called on standard input

source: Error while reading file '/usr/local/bin/autovenv.sh'

Will attempt some more debugging.