mod: update [email protected]

[calvn]

The changes from #10189 seem to have indirectly updated the deps on golang.org/x/sys which breaks compat with the gopsutil module, causing the build to fail.

› make dev
==> Checking that build is using go version >= 1.14.7...
==> Using go version 1.14.7...
go: downloading github.com/hashicorp/vault-plugin-auth-jwt v0.7.2-0.20201022174242-a68fde2bb2b6
go: downloading github.com/hashicorp/vault-plugin-database-mongodbatlas v0.1.3-0.20201022222205-830fcbc5fdd2
go: downloading github.com/hashicorp/vault-plugin-database-elasticsearch v0.5.6-0.20201022222154-56454997629c
go: downloading github.com/hashicorp/vault-plugin-database-couchbase v0.1.1-0.20201022222321-52b89dc4ff04
==> Removing old directory...
==> Building...
Number of parallel builds: 15

-->    darwin/amd64: github.com/hashicorp/vault

1 errors occurred:
--> darwin/amd64 error: exit status 2
Stderr: # github.com/shirou/gopsutil/internal/common
../../go/pkg/mod/github.com/shirou/[email protected]+incompatible/internal/common/common_darwin.go:39:3: undefined: unix.SYS___SYSCTL
../../go/pkg/mod/github.com/shirou/[email protected]+incompatible/internal/common/common_darwin.go:57:3: undefined: unix.SYS___SYSCTL

Updating gopsutil to v2.20.9 resolves this build failure.