fix a glitch about string formatting in sample-reads-randomly.py
fix a glitch about string formatting in sample-reads-randomly.py

F1000Research/khmer,souravsingh/khmer,Winterflower/khmer,kdmurray91/khmer,kdmurray91/khmer,Winterflower/khmer,jas14/khmer,jas14/khmer,ged-lab/khmer,jas14/khmer,ged-lab/khmer,souravsingh/khmer,Winterflower/khmer,ged-lab/khmer,F1000Research/khmer,F1000Research/khmer,kdmurray91/khmer,souravsingh/khmer