doc: convert [\--] to [--]

Commit 1c262bb (doc: convert \--option to --option, 2015-05-13)
explains that we used to need to write \--option to play well with older
versions of AsciiDoc, but that we do not support such versions anymore
anyway, and that Asciidoctor literally renders \--.

With [\--], which is used to denote the optional separator between
revisions and paths, Asciidoctor renders the backslash literally.
Change all [\--] to [--]. This changes nothing for AsciiDoc version
8.6.9, but is an improvement for Asciidoctor version 1.5.4.

We use double-dashes in several list entries (\--::). In my testing, it
appears that we do need to use the backslash there, so leave those.

Signed-off-by: Martin Ågren <[email protected]>

Author: Martin Ågren

Documentation/git-log.txt

@@ -9,7 +9,7 @@ git-log - Show commit logs
 SYNOPSIS
 --------
 [verse]
-'git log' [<options>] [<revision range>] [[\--] <path>...]
+'git log' [<options>] [<revision range>] [[--] <path>...]
 
 DESCRIPTION
 -----------
@@ -90,7 +90,7 @@ include::line-range-format.txt[]
 	ways to spell <revision range>, see the 'Specifying Ranges'
 	section of linkgit:gitrevisions[7].
 
-[\--] <path>...::
+[--] <path>...::
 	Show only commits that are enough to explain how the files
 	that match the specified paths came to be.  See 'History
 	Simplification' below for details and other simplification

Documentation/git-shortlog.txt

@@ -8,7 +8,7 @@ git-shortlog - Summarize 'git log' output
 SYNOPSIS
 --------
 [verse]
-'git shortlog' [<options>] [<revision range>] [[\--] <path>...]
+'git shortlog' [<options>] [<revision range>] [[--] <path>...]
 git log --pretty=short | 'git shortlog' [<options>]
 
 DESCRIPTION
@@ -69,7 +69,7 @@ them.
 	ways to spell <revision range>, see the "Specifying Ranges"
 	section of linkgit:gitrevisions[7].
 
-[\--] <path>...::
+[--] <path>...::
 	Consider only commits that are enough to explain how the files
 	that match the specified paths came to be.
 +

Documentation/gitk.txt

@@ -8,7 +8,7 @@ gitk - The Git repository browser
 SYNOPSIS
 --------
 [verse]
-'gitk' [<options>] [<revision range>] [\--] [<path>...]
+'gitk' [<options>] [<revision range>] [--] [<path>...]
 
 DESCRIPTION
 -----------