Docs with Sphinx are not compiling on Travis
This is the error message:

```
/home/travis/build/StingraySoftware/stingray/stingray/__init__.py:docstring of stingray.AveragedPowerspectrum:5: ERROR: Unexpected indentation.
```

Should be easy to cope with this.

diff --git a/stingray/powerspectrum.py b/stingray/powerspectrum.py
index 5f99a84f..6515fcb4 100755
--- a/stingray/powerspectrum.py
+++ b/stingray/powerspectrum.py
@@ -493,6 +493,7 @@ class AveragedPowerspectrum(Powerspectrum):
         Make an averaged periodogram from a light curve by segmenting the light
         curve, Fourier-transforming each segment and then averaging the
         resulting periodograms.
+
         Parameters
         ----------
         lc: lightcurve.Lightcurve object OR
['stingray/powerspectrum.py']