Fix package() method signature for repositories

poetry/repositories/base_repository.py

@@ -13,7 +13,7 @@ class BaseRepository(object):
     def has_package(self, package):
         raise NotImplementedError()
 
-    def package(self, name, version):
+    def package(self, name, version, extras=None):
         raise NotImplementedError()
 
     def find_packages(self, name, constraint=None, extras=None):

poetry/repositories/repository.py

@@ -18,7 +18,7 @@ class Repository(BaseRepository):
         for package in packages:
             self.add_package(package)
 
-    def package(self, name, version):
+    def package(self, name, version, extras=None):
         name = name.lower()
         version = str(parse_version(version))