arq5x/filo — pull request #7 by slowkow (2013-07-29 02:59:51+00:00)
Title: omit trailing comma with collapse operation

Before

```
$ groupBy -i ex1.out -g 1,2,3,4 -c 8,9 -o collapse,mean
chr1 10 20 A B.1,B.2, 5500
```

After

```
$ groupBy -i ex1.out -g 1,2,3,4 -c 8,9 -o collapse,mean
chr1 10 20 A B.1,B.2 5500
```