[dwm] setmwfact bug

[Szabolcs Nagy]

there's a typo in in dwm.c in setmwfact():

...
else if(1 == sscanf(arg, "%lf", &delta)) {
    if(arg[0] == '+' || arg[0] == '-')
        mwfact += delta;
    else
        mwfact = delta; // should be -=
    ...
}