incorrect dimension reduction

I think lsa.py file has an error, currently it's

```
            #Dimension reduction, build SIGMA'
            for index in xrange(rows - dimensions, rows):
                sigma[index] = 0
```

shouldn't it be:

```
        for index in xrange(dimensions, rows):
            print('setting index to 0 - ', index)
```

The way it is now, a lower dimension will cause better/more precise results.
