docs(di): fix missing export for dgeni docgen

Author: naomiblack

modules/angular2/di.ts

@@ -9,7 +9,7 @@ export * from './src/di/annotations';
 export * from './src/di/decorators';
 export * from './src/di/forward_ref';
 export {resolveBindings, Injector} from './src/di/injector';
-export {Binding, ResolvedBinding, Dependency, bind} from './src/di/binding';
+export {Binding, BindingBuilder, ResolvedBinding, Dependency, bind} from './src/di/binding';
 export {Key, KeyRegistry, TypeLiteral} from './src/di/key';
 export {
   NoBindingError,