add ".in" to escapeurl suffix, use "go vet"

escapeurl.md should've been called escapeurl.in.md. This change
fixes that.

Start using "go vet" instead of "go tool vet" in .travis.yml,
since the latter has been deprecated as of Go 1.12.

.travis.yml

@@ -12,6 +12,6 @@ install:
 script:
   - go get -t -v ./...
   - diff -u <(echo -n) <(gofmt -d -s .)
-  - go tool vet .
+  - go vet ./...
   - go test -v -race ./...
   - diff -u <(echo -n) <(markdownfmt -d README.md)

markdown/main_test.go

@@ -94,7 +94,7 @@ func Test(t *testing.T) {
 		}
 		name := strings.TrimSuffix(fi.Name(), ".in.md")
 		t.Run(name, func(t *testing.T) {
-			got, err := markdown.Process(filepath.Join("testdata", fi.Name()), nil, nil)
+			got, err := markdown.Process(filepath.Join("testdata", name+".in.md"), nil, nil)
 			if err != nil {
 				t.Fatal("markdown.Process:", err)
 			}