Fix multi document YAML restructure issue

Fixes #133

Add explicit delimiter to separate different documents in a YAML file.

assets/issues/issue-133/input.yml

@@ -0,0 +1,13 @@
+---
+bar: foo
+foo: bar
+name: one
+
+---
+Foo: Bar
+name: two
+Bar: Foo
+
+---
+foobar: foobar
+name: three

internal/cmd/cmds_test.go

@@ -72,6 +72,23 @@ list:
 - name: one
   aaa: bbb
 
+`))
+				})
+
+				It("should write a YAML file with multiple documents to STDOUT using restructure feature", func() {
+					out, err := dyff("yaml", "--plain", "--restructure", assets("issues", "issue-133", "input.yml"))
+					Expect(err).ToNot(HaveOccurred())
+					Expect(out).To(BeEquivalentTo(`---
+name: one
+bar: foo
+foo: bar
+---
+name: two
+Foo: Bar
+Bar: Foo
+---
+name: three
+foobar: foobar
 `))
 				})
 			})
@@ -91,7 +108,8 @@ list:
 
 					data, err := ioutil.ReadFile(filename)
 					Expect(err).To(BeNil())
-					Expect(string(data)).To(BeEquivalentTo(`list:
+					Expect(string(data)).To(BeEquivalentTo(`---
+list:
   - name: one
     aaa: bbb
 `))

internal/cmd/common.go

@@ -130,6 +130,7 @@ func (w *OutputWriter) write(writer io.Writer, filename string) error {
 			fmt.Fprintf(writer, "%s\n", output)
 
 		case w.PlainMode && w.OutputStyle == "yaml":
+			fmt.Fprintln(writer, "---")
 			encoder := yamlv3.NewEncoder(writer)
 			encoder.SetIndent(2)
 			encoder.Encode(document)