Merge branch 'ja/tutorial-asciidoctor-fix' into maint

A literal block in the tutorial had lines with unequal lengths to
delimit it from the rest of the document, which choke GitHub's
AsciiDoc renderer.

* ja/tutorial-asciidoctor-fix:
  doc: fix unmatched code fences

Documentation/gitcore-tutorial.txt

@@ -259,7 +259,7 @@ index 557db03..263414f 100644
 @@ -1 +1,2 @@
  Hello World
 +It's a new day for git
-----
+------------
 
 i.e. the diff of the change we caused by adding another line to `hello`.