Adjust syntax for parametrize documentation

Without the double colon, reStructuredText won't display treat the block that
follows as pre-formatted text. Also, with this change comes the need to change a
tab to spaces to align it with the adjacent lines.

--HG--
branch : dirn/adjust-syntax-for-parametrize-documentat-1380671670976

doc/en/skipping.txt

@@ -183,7 +183,7 @@ Skip/xfail with parametrize
 ---------------------------
 
 It is possible to apply markers like skip and xfail to individual
-test instances when using parametrize:
+test instances when using parametrize::
 
      import pytest
 
@@ -191,7 +191,7 @@ test instances when using parametrize:
          (1, 2),
 	 pytest.mark.xfail((1, 0)),
 	 pytest.mark.xfail(reason="some bug")((1, 3)),
-	 (2, 3),
+         (2, 3),
          (3, 4),
          (4, 5),
          pytest.mark.skipif("sys.version_info >= (3,0)")((10, 11)),