Change order of gradle dependencies

Running `gradle build` results in this error:

```console
FAILURE: Build failed with an exception.

* What went wrong:
Could not resolve all dependencies for configuration ':compile'.
> Could not download artifact 'javax.media:jai_core:1.1.3:jai_core.jar'
> Artifact 'javax.media:jai_core:1.1.3:jai_core.jar' not found.
```

Fixed by moving the geotools repo above maven central. From some quick googling, this seemed to be a common problem.