add travis testing support

Well in this case I have a strong opinion that more verbose is better.  Just look at the current logs - once you trim all the standard Travis crap, you get

```
$ rake
The command "rake" exited with 0.
Done. Your build exited with 0.
```

which is virtually useless.  The rake task could be failing to check any files and you would never even notice.

Another reason to get rid of the `grep` is that Ruby could emit warnings before outputting `Syntax OK`.  In that case the `Syntax OK` would be stripped, which would probably mislead the person debugging into looking for a syntax error.

Finally, it should output which files are being checked.  So I suggest:

```
  system('for f in `find -name \*.rb` ; do echo "Syntax checking $f ..."; ruby -c $f || exit $?; done')
```