Updated some conference logos to make their background transparent

archive/entries/2018-06-18-1.xml

@@ -7,7 +7,7 @@
   <default:finalTeaserDate xmlns="http://php.net/ns/news">2018-09-28</default:finalTeaserDate>
   <category term="conferences" label="Conference announcement"/>
   <link href="http://php.net/conferences/index.php#id2018-06-18-1" rel="alternate" type="text/html"/>
-  <default:newsImage xmlns="http://php.net/ns/news" link="https://london2018.live.symfony.com/" title="SymfonyLive London 2018 Conference">symfony-live-london-2018.jpg</default:newsImage>
+  <default:newsImage xmlns="http://php.net/ns/news" link="https://london2018.live.symfony.com/" title="SymfonyLive London 2018 Conference">symfony-live-london-2018.png</default:newsImage>
   <link href="https://london2018.live.symfony.com/" rel="via" type="text/html"/>
   <content type="xhtml">
     <div xmlns="http://www.w3.org/1999/xhtml">

archive/entries/2018-06-25-2.xml

@@ -7,7 +7,7 @@
   <default:finalTeaserDate xmlns="http://php.net/ns/news">2018-10-11</default:finalTeaserDate>
   <category term="conferences" label="Conference announcement"/>
   <link href="http://php.net/conferences/index.php#id2018-06-25-2" rel="alternate" type="text/html"/>
-  <default:newsImage xmlns="http://php.net/ns/news" link="https://usa2018.live.symfony.com/" title="SymfonyLive USA 2018 Conference">symfony-live-usa-2018.jpg</default:newsImage>
+  <default:newsImage xmlns="http://php.net/ns/news" link="https://usa2018.live.symfony.com/" title="SymfonyLive USA 2018 Conference">symfony-live-usa-2018.png</default:newsImage>
   <link href="https://usa2018.live.symfony.com/" rel="via" type="text/html"/>
   <content type="xhtml">
     <div xmlns="http://www.w3.org/1999/xhtml">

archive/entries/2018-06-25-4.xml

@@ -7,7 +7,7 @@
   <default:finalTeaserDate xmlns="http://php.net/ns/news">2018-12-06</default:finalTeaserDate>
   <category term="conferences" label="Conference announcement"/>
   <link href="http://php.net/conferences/index.php#id2018-06-25-4" rel="alternate" type="text/html"/>
-  <default:newsImage xmlns="http://php.net/ns/news" link="https://lisbon2018.symfony.com/" title="SymfonyCon Lisbon 2018 Conference">symfony-con-lisbon-2018.jpg</default:newsImage>
+  <default:newsImage xmlns="http://php.net/ns/news" link="https://lisbon2018.symfony.com/" title="SymfonyCon Lisbon 2018 Conference">symfony-con-lisbon-2018.png</default:newsImage>
   <link href="https://lisbon2018.symfony.com/" rel="via" type="text/html"/>
   <content type="xhtml">
     <div xmlns="http://www.w3.org/1999/xhtml">
@@ -16,7 +16,7 @@
      bring the entire community to Portugal and discover the amazing city of Lisbon.
      If you like Symfony and share fun with professionals, this is where you want to
      be on December!</p>
-     
+
      <p>We look forward to welcoming you to Lisbon, capital of Portugal and bordered
      by the Atlantic Ocean. Join us for talks, workshops, discussions and other
      serious work around Symfony and its environment, then sharing this very special