[mod] documentations & comments: update http://* URL to https://*.

About http://lesscss.org see https://github.com/less/less-docs/issues/520

docs/admin/buildhosts.rst

@@ -67,7 +67,7 @@ to ``imgmath``:
 If your docs build (``make docs``) shows warnings like this::
 
    WARNING: dot(1) not found, for better output quality install \
-            graphviz from http://www.graphviz.org
+            graphviz from https://www.graphviz.org
    ..
    WARNING: LaTeX command 'latex' cannot be run (needed for math \
             display), check the imgmath_latex setting

docs/admin/installation-nginx.rst

@@ -9,7 +9,7 @@ Install with nginx
 .. _nginx server configuration:
    https://docs.nginx.com/nginx/admin-guide/web-server/web-server/#setting-up-virtual-servers
 .. _nginx beginners guide:
-   http://nginx.org/en/docs/beginners_guide.html
+   https://nginx.org/en/docs/beginners_guide.html
 .. _Getting Started wiki:
    https://www.nginx.com/resources/wiki/start/
 .. _uWSGI support from nginx:

docs/admin/settings.rst

@@ -112,7 +112,7 @@ Global Settings
   specific instance of searx, a locale can be defined using an ISO language
   code, like ``fr``, ``en``, ``de``.
 
-.. _requests proxies: http://requests.readthedocs.io/en/latest/user/advanced/#proxies
+.. _requests proxies: https://requests.readthedocs.io/en/latest/user/advanced/#proxies
 .. _PySocks: https://pypi.org/project/PySocks/
 
 ``proxies`` :