fix little bug "[[ ! ]] /usr/bin/screenfetch: line 817: [: 2415.7: integer expression expected"

before this change an error message was displayed on my installation:

[anakin@DeathStar]$ screenfetch 
[ ! ]] /usr/bin/screenfetch: line 817: [: 2415.7: integer expression expected
                   -`
                  .o+`                 anakin@DeathStar
                 `ooo/                 OS: Arch Linux 
                `+oooo:                Kernel: x86_64 Linux 3.14.25-1-lts
 [...]

Now seems work well... :)