Explicitly set excludeTrailingPunctuationFromURLs to true in showdown config

src/sidebar/render-markdown.js

@@ -31,6 +31,7 @@ function renderMarkdown(markdown) {
     converter = new showdown.Converter({
       extensions: [targetBlank],
       simplifiedAutoLink: true,
+      excludeTrailingPunctuationFromURLs: true,
       // Since we're using simplifiedAutoLink we also use
       // literalMidWordUnderscores because otherwise _'s in URLs get
       // transformed into <em>'s.

src/sidebar/test/render-markdown-test.js

@@ -45,6 +45,16 @@ describe('render-markdown', () => {
           'https://hypothes.is/stream?q=tag:group_test_needs_card</a></p>'
       );
     });
+
+    ['.', ',', '!', '?'].forEach(symbol => {
+      it('should autolink URLs excluding trailing punctuation symbols', () => {
+        assert.equal(
+          render(`See this link - http://arxiv.org/article${symbol}`),
+          '<p>See this link - <a href="http://arxiv.org/article" target="_blank">' +
+            `http://arxiv.org/article</a>${symbol}</p>`
+        );
+      });
+    });
   });
 
   describe('markdown rendering', () => {