fix refernce to cosmology

examples/injection_examples/fast_tutorial.py

@@ -5,7 +5,7 @@ space for an injected signal.
 
 This example estimates the masses using a uniform prior in both component masses
 and distance using a uniform in comoving volume prior on luminosity distance
-between luminosity distances of 100Mpc and 5Gpc, the cosmology is WMAP7.
+between luminosity distances of 100Mpc and 5Gpc, the cosmology is Planck15.
 """
 from __future__ import division, print_function