Update ale2wiggle.py

The output was not conform the .wig description as found on https://genome.ucsc.edu/goldenPath/help/wiggle.html when working with a file consisting of multiple contigs/scaffolds.
Update fixes the problem and allows converting with wigToBigWig tool.
Merge pull request #10 from holmrenser/master

Update ale2wiggle.py
Thanks for your help!