Merge pull request #519 from bollwyvl/patch-2

Address syntax warning for use of "is" against a string literal

Author: kevin-bates

jupyter_client/manager.py

@@ -79,7 +79,7 @@ def _kernel_name_changed(self, change):
 
     @property
     def kernel_spec(self):
-        if self._kernel_spec is None and self.kernel_name is not '':
+        if self._kernel_spec is None and self.kernel_name != '':
             self._kernel_spec = self.kernel_spec_manager.get_kernel_spec(self.kernel_name)
         return self._kernel_spec