outside_limits? method in MonitorUtilities has an error in logic causing false positives #12
Description
This line: https://github.com/livingsocial/rearview-engine/blob/master/lib/rearview/templates/utilities.rb#L43, where it says "diffs.length == 2" will always result in a false returned unless exactly two comparison_values are passed in to the parameters. This means that if I want to call the #percentage_errors method and compare today's data against last week's, two weeks ago's, and three weeks ago's, the percentage_errors will be zero, even if there are multiple errors, since I'm passing in 3 comparison metrics instead of two.