bat: fix broken battery remaining time (was always N/A)

Bug was introduced in commit dc556e5 and the new discharging
symbol.

Signed-off-by: Adrian C. (anrxc) <anrxc@sysphere.org>

widgets/bat.lua

@@ -74,7 +74,7 @@ local function worker(format, warg)
     if rate ~= nil and rate ~= 0 then
         if state == "+" then
             timeleft = (tonumber(capacity) - tonumber(remaining)) / tonumber(rate)
-        elseif state == "-" then
+        elseif state == "−" then
             timeleft = tonumber(remaining) / tonumber(rate)
         else
             return {state, percent, time, wear}