Fixed `haxelib path ...` parsing.

Currently `haxelib path hxcpp` gives:
```
path/to/hxcpp/
-D hxcpp=3.1.0
```
Notice there is version number at the end of `-D`.

I discovered this on Windows, when I `haxelib dev hxcpp ...` and `haxelib run hxcpp` (with no arg).
Not sure why it worked on Mac and Linux...