Bump widget protocol version number back to 2.1.0

Author: jasongrout

packages/base-manager/test/src/manager_test.ts

@@ -180,7 +180,7 @@ describe('ManagerBase', function () {
           },
         },
         metadata: {
-          version: '3.0.0',
+          version: '2.1.0',
         },
       });
       expect(model.comm).to.equal(comm);
@@ -243,7 +243,7 @@ describe('ManagerBase', function () {
         },
         buffers: [new DataView(new Uint8Array([1, 2, 3]).buffer)],
         metadata: {
-          version: '3.0.0',
+          version: '2.1.0',
         },
       });
       expect(model.comm).to.equal(comm);

packages/base/src/version.ts

@@ -3,4 +3,4 @@
 
 export const JUPYTER_WIDGETS_VERSION = '2.0.0';
 
-export const PROTOCOL_VERSION = '3.0.0';
+export const PROTOCOL_VERSION = '2.1.0';

python/ipywidgets/ipywidgets/_version.py

@@ -3,7 +3,7 @@
 
 __version__ = '8.0.0b1'
 
-__protocol_version__ = '3.0.0'
+__protocol_version__ = '2.1.0'
 __control_protocol_version__ = '1.0.0'
 
 # These are *protocol* versions for each package, *not* npm versions. To check, look at each package's src/version.ts file for the protocol version the package implements.