format code with gofumpt

gofumpt (https://github.com/mvdan/gofumpt) provides a supserset of `gofmt` / `go fmt`,
and addresses various formatting issues that linters may be checking for.

We can consider enabling the `gofumpt` linter to verify the formatting in CI, although
not every developer may have it installed, so for now this runs it once to get formatting
in shape.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

manifest/schema1/manifest_test.go

@@ -42,7 +42,6 @@ func TestManifestUnmarshaling(t *testing.T) {
 	if !reflect.DeepEqual(&signed, env.signed) {
 		t.Fatalf("manifests are different after unmarshaling: %v != %v", signed, env.signed)
 	}
-
 }
 
 func TestManifestVerification(t *testing.T) {