include stale data in the adjustment used for the threshold lines

[jasoncalabrese]

fixes a bug where the lines don't get transitioned to the right edge when data is stale

[codecov-io]

Current coverage is 82.08%

Merging #796 into dev will decrease coverage by -0.01% as of 1e456cb

@@              dev    #796   diff @@
=====================================
  Files          60      60       
  Stmts        4014    4013     -1
  Branches        0       0       
  Methods         0       0       
=====================================
- Hit          3295    3294     -1
  Partial         0       0       
  Missed        719     719       

Review entire Coverage Diff as of 1e456cb

---

Uncovered Suggestions

1. +0.35% via lib/mqtt.js#128...141
2. +0.30% via ...rofile/js/profile.js#321...332
3. +0.30% via lib/mqtt.js#292...303
4. See 7 more...

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