Prevent pkill commands from ranking high

Thank you for the nice work on this project. I did the pull request twice because i messed up with github a little bit. Let me explain what i changed: I use rofi many times to kill programs, thus many times the pkill commands gets higher ranked than the original command. For example if i do "pkill linphone" too many times with rofi, "pkill linphone" is higher than the linphone command.  I find this inconvenient. I think these should be in the cache history but not rank high. For this reason I created a simple modification of your source code. what it does is it checks if pkill is in the command to be run and if so it puts index =1.