Werk #5956: Updated NagVis to 1.9.7

Component	Other components
Title	Updated NagVis to 1.9.7
Date	Apr 6, 2018
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	1.5.0b1 Checkmk Community, Checkmk Pro, Checkmk Ultimate MT

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