docs: handle double colon in linkgit:: gracefully

Accommodate for versions before 1cca17dfff48 (Documentation: fix linkgit
references, 2016-05-04): there were double colons in `linkgit::`
constructs.

Since we want to build older versions' manual pages, we will have to
handle those since-fixed mistakes gracefully.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

script/update-docs.rb

@@ -349,8 +349,8 @@ def index_doc(filter_tags, doc_list, get_content)
 
         # Generate HTML
         html = asciidoc.render
-        html.gsub!(/linkgit:(\S+?)\[(\d+)\]/) do |line|
-          x = /^linkgit:(\S+?)\[(\d+)\]/.match(line)
+        html.gsub!(/linkgit:+(\S+?)\[(\d+)\]/) do |line|
+          x = /^linkgit:+(\S+?)\[(\d+)\]/.match(line)
           relurl = "docs/#{x[1].gsub(/-/, '-')}"
           "<a href='{{< relurl \"#{relurl}\" >}}'>#{x[1]}[#{x[2]}]</a>"
         end