fix: update doi.org links according to http://blog.crossref.org/2016/09/new-crossref-doi-display-guidelines.html. (#69)

bibtexbrowser-test.php

@@ -302,7 +302,7 @@ class BTBTest extends PHPUnit_Framework_TestCase {
     $btb = new BibDataBase();
     $btb->update_internal("inline", $test_data);
     $first_entry=$btb->bibdb[array_keys($btb->bibdb)[0]];
-    $this->assertEquals('<pre class="purebibtex">@Article{Baldwin2014Quantum,Doi={<a href="https://dx.doi.org/10.1103/PhysRevA.90.012110">10.1103/PhysRevA.90.012110</a>},Url={<a href="http://link.aps.org/doi/10.1103/PhysRevA.90.012110">http://link.aps.org/doi/10.1103/PhysRevA.90.012110</a>}}</pre>',$first_entry->toEntryUnformatted());
+    $this->assertEquals('<pre class="purebibtex">@Article{Baldwin2014Quantum,Doi={<a href="https://doi.org/10.1103/PhysRevA.90.012110">10.1103/PhysRevA.90.012110</a>},Url={<a href="http://link.aps.org/doi/10.1103/PhysRevA.90.012110">http://link.aps.org/doi/10.1103/PhysRevA.90.012110</a>}}</pre>',$first_entry->toEntryUnformatted());
   }
 
   function test_filter_view() {

bibtexbrowser.php

@@ -1336,7 +1336,7 @@ class BibEntry {
   function getDoiLink($iconurl=NULL) {
     $str = $this->getIconOrTxt('doi',$iconurl);
     if ($this->hasField('doi')) {
-        return '<a'.get_target().' href="https://dx.doi.org/'.$this->getField('doi').'">'.$str.'</a>';
+        return '<a'.get_target().' href="https://doi.org/'.$this->getField('doi').'">'.$str.'</a>';
     }
     return '';
   }
@@ -1901,7 +1901,7 @@ class BibEntry {
 
     // Fields that should be hyperlinks
     // the order matters
-    $hyperlinks = array('url' => '%O', 'file' => '%O', 'pdf' => '%O', 'doi' => 'https://dx.doi.org/%O', 'gsid' => 'https://scholar.google.com/scholar?cites=%O');
+    $hyperlinks = array('url' => '%O', 'file' => '%O', 'pdf' => '%O', 'doi' => 'https://doi.org/%O', 'gsid' => 'https://scholar.google.com/scholar?cites=%O');
 
     $vals = array();
     foreach ($hyperlinks as $field => $url) {