Update gometalinter config (#331)

* Update gometalinter config

gometalinter now uses `maligned` instead of `aligncheck`
(https://github.com/alecthomas/gometalinter/pull/367), so we need to update our
config accordingly.

* Update gometalinter

* Disable gotype linter

gotype does not seem to play nicely with the gb vendor directory. In
particular, it wants each of our dependencies to be built and installed (see
https://github.com/golang/go/issues/10969), but (empirically) it will not
accept them being installed in `pkg` but insists on them being in `vendor/pkg`.

This presents a problem because `gb build` builds the packages into `pkg`
(which doesn't seem entirely unreasonable since `.` comes before `vendor` in
`$GOPATH`). `go install github.com/x/y` does install in `vendor/pkg` but
requires us to know the name of each package.

The general conclusion of https://github.com/alecthomas/gometalinter/issues/91
seems to have been that the easiest thing to do is to disable `gotype` for now.

* Fix `unparam` lint

* Fix goshadow lint

linter.json

@@ -4,13 +4,12 @@
     "Deadline": "5m",
     "Enable": [
         "vetshadow",
-        "gotype",
         "deadcode",
         "gocyclo",
         "golint",
         "varcheck",
         "structcheck",
-        "aligncheck",
+        "maligned",
         "ineffassign",
         "gas",
         "misspell",