more space between bottom icons (root-project#537)

Author: couet

_includes/footer/custom.html

@@ -6,26 +6,31 @@
         <img style="width:auto; height:2em;" src="{{'/assets/images/forum2.svg' | relative_url}}"></a></div>
         <div><font color="#346295" " size="1">Forum</font></div>
     </div>
+    <div style="display:inline-block;"><span style="opacity:0;">space</span></div>
     <div style="display:inline-block;">
         <div><a href="https://github.com/root-project/root/issues/new" target="_blank" title="File a bug report">
         <img style="width:auto; height:2em;" src="{{'/assets/images/bug.svg' | relative_url}}"></a></div>
         <div><font color="#346295" " size="1">Bug</font></div>
     </div>
+    <div style="display:inline-block;"><span style="opacity:0;">space</span></div>
     <div style="display:inline-block;">
         <div><a href="mailto:[email protected]" target="_blank" title="Send an email to [email protected]">
         <img style="width:auto; height:2em;" src="{{'/assets/images/mail.svg' | relative_url}}"></a></div>
         <div><font color="#346295" " size="1">Mail</font></div>
     </div>
+    <div style="display:inline-block;"><span style="opacity:0;">space</span></div>
     <div style="display:inline-block;">
         <div><a href="https://github.com/root-project" target="_blank" title="">
         <img style="width:auto; height:2em;" src="{{'/assets/images/Github.svg' | relative_url}}"></a></div>
         <div><font color="#346295" " size="1">GitHub</font></div>
     </div>
+    <div style="display:inline-block;"><span style="opacity:0;">space</span></div>
     <div style="display:inline-block;">
         <div><a href="{% if site.atom_feed.path %}{{ site.atom_feed.path }}{% else %}{{ '/feed.xml' | relative_url }}{% endif %}">
         <img style="width:auto; height:2em;" src="{{'/assets/images/feed.svg' | relative_url}}"></a></div>
         <div><font color="#346295" " size="1">Feed</font></div>
     </div>
+    <div style="display:inline-block;"><span style="opacity:0;">space</span></div>
     <div style="display:inline-block;">
         <div><a href="https://twitter.com/ROOT_Project">
         <img style="width:auto; height:2em;" src="{{'/assets/images/twitter.svg' | relative_url}}"></a></div>