Fix formatting of git-blame documentation.

blame-options.txt did not format multi-paragraph option description
correctly.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/blame-options.txt

@@ -64,7 +64,7 @@ of lines before or after the line given by <start>.
 	assigns blame to the lines that were moved down (i.e. A)
 	to the child commit.  With this option, both groups of lines
 	are blamed on the parent.
-
++
 <num> is optional but it is the lower bound on the number of
 alphanumeric characters that git must detect as moving
 within a file for it to associate those lines with the parent
@@ -77,7 +77,7 @@ of lines before or after the line given by <start>.
 	around across files.  When this option is given twice,
 	the command looks for copies from all other files in the
 	parent for the commit that creates the file in addition.
-
++
 <num> is optional but it is the lower bound on the number of
 alphanumeric characters that git must detect as moving
 between files for it to associate those lines with the parent