fix blank output in tmux when using fish shell

[anark]

Hello,
When using dispatch with Fish shell set I get an empty output in all tmux windows while the command is running.

This fixes the output so the output shows while it is running.

[tpope]

It was definitely added for a reason. Please blame the line and find the commit that added it so I can see if it's still relevant.

[anark]

It was added in the commit to support fish shell(4566b88) and close the blank output issue(#217). However when I run Dispatch without this change the output in the tmux pane is blank. When I run it with this change the output displays correctly.

[tpope]

Okay, since it was added with the rest of the Fish support I assume it was just based on my personal testing. I'm okay to remove it.

The real issue, though, appears to be a broken Fish behavior. The following command won't output anything until 10 seconds later after the entire begin block has finished running:

begin; echo test; sleep 10; end | cat

Appears to be a longstanding issue. fish-shell/fish-shell#1396