Added missing comma to henplus recipe

Fixes the following error:

```
==> Downloading https://github.com/downloads/neurolabs/henplus/henplus-0.9.8.tar.gz
######################################################################## 100.0%
==> ant install-Dprefix=/usr/local/Cellar/henplus/0.9.8

BUILD FAILED
Target "install-Dprefix=/usr/local/Cellar/henplus/0.9.8" does not exist in the project "HenPlus".
```