monoblue: use padding instead of position for text in footer

Some installations alter monoblue style and remove margins from body element
(these margins have that dark gray background) to adapt hgweb instance to an
already existing site design. However, the margins hid a quirk in page footer:
a block of text needlessly popped out of the footer, and when margins were
gone, the whole page got a vertical scroll bar because of that.

Live example: https://hg.prosody.im/prosody-modules/

To remove the potential scroll bar, this block of text now uses left padding,
which doesn't make it overflow the footer, but makes it achieve the otherwise
same result visually.

mercurial/templates/static/style-monoblue.css

@@ -153,7 +153,7 div.page-footer {
 }
   div.page-footer p {
     position: relative;
-    left: 20px;
+    padding-left: 20px;
     bottom: 5px;
     font-size: 1.2em;
   }