Added sonatype repositories - to support Lift 2.6-SNAPSHOT

Lift 2.6-SNAPSHOT jars are not on maven (not sure why), so escalante cannot find them if your app runs on 2.6.

I added the sonatype repos, hoping it will fix it.

I tried building this but I get

```
[ERROR] Failed to execute goal net.alchim31.maven:scala-maven-plugin:3.1.3:script (scala-magic) on project escalante-assembly: Execution scala-magic of goal net.alchim31.maven:scala-maven-plugin:3.1.3:script failed. NullPointerException -> [Help 1]

```

Thanks

  Diego