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

vendor/src/github.com/alecthomas/gometalinter/regressiontests/nakedret_test.go

@@ -0,0 +1,29 @@
+package regressiontests
+
+import "testing"
+
+func TestNakedret(t *testing.T) {
+	t.Parallel()
+	source := `package test
+
+func shortFunc() (r uint32) {
+	r = r + r
+	return
+}
+	
+func longFunc() (r uint32) {
+	r = r + r
+	r = r - r
+	r = r * r
+	r = r / r
+	r = r % r
+	r = r^r
+	r = r&r
+	return
+}	
+`
+	expected := Issues{
+		{Linter: "nakedret", Severity: "warning", Path: "test.go", Line: 16, Message: "longFunc naked returns on 9 line function "},
+	}
+	ExpectIssues(t, "nakedret", source, expected)
+}