Arch Linux

Description:
The bash completion file for optirun is not loaded due to the usage of an old operator (`have`) within the completion scripts.
Using the updated one (`_have`) solves the issue.

Additional info:
* package version(s):
```
$ pacman -Qs bash
...
local/bash 4.4.023-1 (base)
The GNU Bourne Again shell
local/bash-completion 2.8-1
Programmable completion for the bash shell
...
$ pacman -Qs bumblebee
local/bumblebee 3.2.1-17
NVIDIA Optimus support for Linux through VirtualGL
...
```

Steps to reproduce:
1. Install the above mentioned packages.
2. Try to complete the optirun command using Tab.

Expected:
Show the available system commands

Result:
The files in the local folder are shown.

Fix:
Replacing `have` with `_have` in the completion file fixes the issue.
The file is:
/usr/share/bash-completion/completions/optirun

Additional comment:
Testing for the command to exists is not useful, as it is present within the same package.