Fix percent calculation

[ChuntaoLu]

current way of computing percentage leads to falsy 100% coverage when numbers are big, e.g.,

> function percent(covered, total) {
...         var tmp;
...         if (total > 0) {
.....             tmp = 1000 * 100 * covered / total + 5;
.....             return Math.floor(tmp / 10) / 100;
.....         } else {
.....             return 100.00;
.....         }
...     }
undefined
> percent(20000, 20001)
100

Proposed fix:

> function percent(covered, total) {
...         var tmp;
...         if (total > 0) {
.....             return Math.floor(10000 * covered / total) / 100;
.....         } else {
.....             return 100.00;
.....         }
...     }
undefined
> percent(20000, 20001)
99.99
> percent(200000, 200001)
99.99

[coveralls]

Coverage decreased (-0.002%) to 97.521% when pulling d44c89e9eeee2dd1843d8421fc34c22baa7f9894 on ChuntaoLu:fix-percent into 89e338fcb1c8a7dea3b9e8f851aa55de2bc3abee on gotwarlost:master.