resolve #232: open browser linux compatibility

@kevgo 

Able to test by overriding the `which` command to fake what tools are installed on the system.
The `tools` variable belongs to the code block below. I would move the empty line up like this:

```bash
local url=$1

local tools=(open xdg-open)
for tool in "${tools[@]}"; do
   if [ "$(has_tool "$tool")" = true ]; then
     eval "$tool $url"
     return
   fi
 done