gopsutil: bump to fix vendoring problem

This was fixed here shirou/gopsutil#889

We use go mod vendor in NixOS to archive all dependencies and allow
reproducible offline builds.

Changelog is minimal otherwise:

- https://github.com/shirou/gopsutil/releases/tag/v2.20.6

go.mod

@@ -110,7 +110,7 @@ require (
 	github.com/safchain/ethtool v0.0.0-20200218184317-f459e2d13664
 	github.com/samuel/go-zookeeper v0.0.0-20180130194729-c4fab1ac1bec // indirect
 	github.com/satori/go.uuid v1.2.1-0.20181028125025-b2ce2384e17b // indirect
-	github.com/shirou/gopsutil v2.20.5+incompatible
+	github.com/shirou/gopsutil v2.20.6+incompatible
 	github.com/shopspring/decimal v0.0.0-20200105231215-408a2507e114 // indirect
 	github.com/sirupsen/logrus v1.4.2
 	github.com/soniah/gosnmp v1.25.0

go.sum

@@ -520,8 +520,8 @@ github.com/samuel/go-zookeeper v0.0.0-20180130194729-c4fab1ac1bec h1:6ncX5ko6B9L
 github.com/samuel/go-zookeeper v0.0.0-20180130194729-c4fab1ac1bec/go.mod h1:gi+0XIa01GRL2eRQVjQkKGqKF3SF9vZR/HnPullcV2E=
 github.com/sean-/seed v0.0.0-20170313163322-e2103e2c3529 h1:nn5Wsu0esKSJiIVhscUtVbo7ada43DJhG55ua/hjS5I=
 github.com/sean-/seed v0.0.0-20170313163322-e2103e2c3529/go.mod h1:DxrIzT+xaE7yg65j358z/aeFdxmN0P9QXhEzd20vsDc=
-github.com/shirou/gopsutil v2.20.5+incompatible h1:tYH07UPoQt0OCQdgWWMgYHy3/a9bcxNpBIysykNIP7I=
-github.com/shirou/gopsutil v2.20.5+incompatible/go.mod h1:5b4v6he4MtMOwMlS0TUMTu2PcXUg8+E1lC7eC3UO/RA=
+github.com/shirou/gopsutil v2.20.6+incompatible h1:P37G9YH8M4vqkKcwBosp+URN5O8Tay67D2MbR361ioY=
+github.com/shirou/gopsutil v2.20.6+incompatible/go.mod h1:5b4v6he4MtMOwMlS0TUMTu2PcXUg8+E1lC7eC3UO/RA=
 github.com/shopspring/decimal v0.0.0-20200105231215-408a2507e114 h1:Pm6R878vxWWWR+Sa3ppsLce/Zq+JNTs6aVvRu13jv9A=
 github.com/shopspring/decimal v0.0.0-20200105231215-408a2507e114/go.mod h1:DKyhrW/HYNuLGql+MJL6WCR6knT2jwCFRcu2hWCYk4o=
 github.com/sirupsen/logrus v1.2.0 h1:juTguoYk5qI21pwyTXY3B3Y5cOTH3ZUyZCg1v/mihuo=