Fix triple slash comments new paragraph spacing.

pkg/docgen/lib/docgen.dart

Index: pkg/docgen/lib/docgen.dart
diff --git a/pkg/docgen/lib/docgen.dart b/pkg/docgen/lib/docgen.dart
index 4c8ffe74ecf7d9497451acfa2352fe6678b02de0..239d08a76056b204a6280ae97ef76727ac68e39f 100644
--- a/pkg/docgen/lib/docgen.dart
+++ b/pkg/docgen/lib/docgen.dart
@@ -343,10 +343,12 @@ void _documentLibraries(List<LibraryMirror> libs, {bool includeSdk: false,
     };
   }
   _writeToFile(JSON.encode(libraryMap), 'library_list.json');
+
   // Output libraries and classes to file after all information is generated.
   filteredEntities.where((e) => e is Class || e is Library).forEach((output) {
     _writeIndexableToFile(output, outputToYaml);
   });
+
   // Outputs all the qualified names documented with their type.
   // This will help generate search results.
   _writeToFile(filteredEntities.map((e) =>
@@ -450,7 +452,7 @@ String _commentToHtml(DeclarationMirror mirror) {
         if (commentText == null) {
           commentText = comment.trimmedText;
         } else {
-          commentText = '$commentText ${comment.trimmedText}';
+          commentText = '$commentText\n${comment.trimmedText}';
         }
       }
     }