fix nadir, + not -, upstream pr#125

use correction suggested by andiling, and implemented over on suncalc3 by Hypnos3

Author: sonicbluesky

suncalc.js

@@ -163,7 +163,7 @@ SunCalc.getTimes = function (date, lat, lng, height) {
 
     var result = {
         solarNoon: fromJulian(Jnoon),
-        nadir: fromJulian(Jnoon - 0.5)
+        nadir: fromJulian(Jnoon + 0.5)
     };
 
     for (i = 0, len = times.length; i < len; i += 1) {