all: update github.com/rcrowley/go-metrics a5cfc242a56b => 51425a2415…

…d2 (#1679)

Update `github.com/rcrowley/go-metrics` for transition to Modules (#1634).

From: rcrowley/go-metrics@a5cfc242a56b
To: rcrowley/go-metrics@51425a2415d2

Diff: rcrowley/go-metrics@a5cfc24...51425a2 (41 commits)

To make the transition to Modules possible. Some dependencies at their current version have incompatible relationships with other dependencies we have. Dep was more tolerant to incompatible versions than Modules. Making this change ahead of the PR that switches us to Modules makes that PR a functional no-op.

The reason Modules is updating `go-metrics` is because the monorepo is also dependent on `github.com/ethereum/go-ethereum` which is in turn, via it's tests, dependent on the `exp` sub-package within `go-metrics`. The sub-package was added in rcrowley/go-metrics@51425a2.

The `go` tool in this situation will automatically upgrade `go-metrics` to it's latest revision since it can see the `exp` is available there. This PR is however upgrading to the first or oldest revision that contains the sub-package we need to satisfy Modules. We could upgrade to the latest revision but the changes in the smaller diff are much less significant and pose a smaller risk than the changes that are in the diff (rcrowley/go-metrics@a5cfc24...cac0b30 144 commits) to take us all the way to latest. 

More details about how this was discovered can be found here: golang/go#33771 (comment)

Gopkg.toml

@@ -88,3 +88,7 @@
 [[constraint]]
   branch = "master"
   name = "github.com/shurcooL/httpfs"
+
+[[constraint]]
+  name = "github.com/rcrowley/go-metrics"
+  revision = "51425a2415d21afadfd55cd93432c0bc69e9598d"