go.mod: bump golang.org/x/sys from 0.6.0 to 0.7.0

Bumps [golang.org/x/sys](https://github.com/golang/sys) from 0.6.0 to 0.7.0.
- [Release notes](https://github.com/golang/sys/releases)
- [Commits](golang/sys@v0.6.0...v0.7.0)

---
updated-dependencies:
- dependency-name: golang.org/x/sys
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

go.mod

@@ -2,4 +2,4 @@ module github.com/tklauser/numcpus
 
 go 1.13
 
-require golang.org/x/sys v0.6.0
+require golang.org/x/sys v0.7.0

go.sum

@@ -1,2 +1,2 @@
-golang.org/x/sys v0.6.0 h1:MVltZSvRTcU2ljQOhs94SXPftV6DCNnZViHeQps87pQ=
-golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.7.0 h1:3jlCCIQZPdOYu1h8BkNvLz8Kgwtae2cagcG/VamtZRU=
+golang.org/x/sys v0.7.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=