Upgrade trestle

pubspec.yaml

@@ -18,10 +18,7 @@ dependencies:
   plato: '>=0.2.0 <1.0.0'
   path: '^1.3.5'
   http_server: '^0.9.5+1'
-  trestle:
-    git:
-      url: https://github.com/dart-bridge/trestle
-      ref: develop
+  trestle: '^0.6.0'
   async: '^1.3.0'
 dev_dependencies:
   test: any