build(deps): bump golang.org/x/sys from 0.1.0 to 0.21.0

Bumps [golang.org/x/sys](https://github.com/golang/sys) from 0.1.0 to 0.21.0.
- [Commits](golang/sys@v0.1.0...v0.21.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

go.mod

@@ -2,4 +2,4 @@ module github.com/photostorm/gatt
 
 go 1.13
 
-require golang.org/x/sys v0.1.0
+require golang.org/x/sys v0.21.0

go.sum

@@ -1,2 +1,2 @@
-golang.org/x/sys v0.1.0 h1:kunALQeHf1/185U1i0GOB/fy1IPRDDpuoOOqRReG57U=
-golang.org/x/sys v0.1.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.21.0 h1:rF+pYz3DAGSQAxAu1CbC7catZg4ebC4UIeIhKxBZvws=
+golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=