Fix for issue affecting some feeds that have datastreams without tags

Only attempt to detect the tags of interest if .tags is not nil on each
datastream
[gem] sinatra 1.3.4
[gem] cosm-rb 0.2.05
[gem] rspec 2.12.0
[gem] sass 3.2.5
[gem] newrelic_rpm 3.5.6.46
[travis] ruby 1.8.7 not supported
[travis] just run tests under mri
Merge pull request #45 from levent/maintenance

Maintenance - Upgrading gems
Merge remote-tracking branch 'upstream/master'