Merge pull request git#2008 from Botato300/patch-1

fix broken links: change from .txt to .adoc

Author: dscho

external/docs/content/docs/howto/maintain-git.html

@@ -1,5 +1,5 @@
 ---
 ### DO NOT EDIT! Generated by script/update-docs.rb
 
-redirect_to: https://github.com/git/git/blob/HEAD/Documentation/howto/maintain-git.txt
+redirect_to: https://github.com/git/git/blob/HEAD/Documentation/howto/maintain-git.adoc
 ---

external/docs/content/docs/howto/revert-a-faulty-merge.html

@@ -1,5 +1,5 @@
 ---
 ### DO NOT EDIT! Generated by script/update-docs.rb
 
-redirect_to: https://github.com/git/git/blob/HEAD/Documentation/howto/revert-a-faulty-merge.txt
+redirect_to: https://github.com/git/git/blob/HEAD/Documentation/howto/revert-a-faulty-merge.adoc
 ---

external/docs/content/docs/howto/setup-git-server-over-http.html

@@ -1,5 +1,5 @@
 ---
 ### DO NOT EDIT! Generated by script/update-docs.rb
 
-redirect_to: https://github.com/git/git/blob/HEAD/Documentation/howto/setup-git-server-over-http.txt
+redirect_to: https://github.com/git/git/blob/HEAD/Documentation/howto/setup-git-server-over-http.adoc
 ---

external/docs/content/docs/howto/update-hook-example.html

@@ -1,5 +1,5 @@
 ---
 ### DO NOT EDIT! Generated by script/update-docs.rb
 
-redirect_to: https://github.com/git/git/blob/HEAD/Documentation/howto/update-hook-example.txt
+redirect_to: https://github.com/git/git/blob/HEAD/Documentation/howto/update-hook-example.adoc
 ---

script/update-docs.rb

@@ -605,7 +605,7 @@ def index_doc(filter_tags, doc_list, get_content)
             type = 'tree'
             target = 'howto'
           else
-            target += '.txt'
+            target += '.adoc'
           end
           front_matter = { "redirect_to" => "https://github.com/git/git/#{type}/HEAD/Documentation/#{target}" } # ltrim `docs/`
           FileUtils.mkdir_p(File.dirname(doc_path))