Fix serialized classNames for Optimizers (#1861)

BUG
INTERNAL

src/optimizers/adadelta_optimizer.ts

@@ -25,7 +25,7 @@ import {Optimizer, OptimizerVariable} from './optimizer';
 /** @doclink Optimizer */
 export class AdadeltaOptimizer extends Optimizer {
   /** @nocollapse */
-  static className = 'AdadeltaOptimizer';
+  static className = 'Adadelta';  // Name matters for Python compatibility.
   private accumulatedGrads: OptimizerVariable[] = [];
   private accumulatedUpdates: OptimizerVariable[] = [];
 

src/optimizers/momentum_optimizer.ts

@@ -28,7 +28,7 @@ import {SGDOptimizer} from './sgd_optimizer';
 /** @doclink Optimizer */
 export class MomentumOptimizer extends SGDOptimizer {
   /** @nocollapse */
-  static className = 'MomentumOptimizer';
+  static className = 'Momentum';  // Name matters for Python compatibility.
   private m: Scalar;
   private accumulations: OptimizerVariable[] = [];
 

src/optimizers/rmsprop_optimizer.ts

@@ -26,7 +26,7 @@ import {Optimizer, OptimizerVariable} from './optimizer';
 /** @doclink Optimizer */
 export class RMSPropOptimizer extends Optimizer {
   /** @nocollapse */
-  static className = 'RMSProp';
+  static className = 'RMSProp';  // Note: Name matters for Python compatibility.
   private centered: boolean;
 
   private accumulatedMeanSquares: OptimizerVariable[] = [];

src/optimizers/sgd_optimizer.ts

@@ -27,7 +27,7 @@ import {Optimizer} from './optimizer';
 /** @doclink Optimizer */
 export class SGDOptimizer extends Optimizer {
   /** @nocollapse */
-  static className = 'SGD';  // Name matters for Python compatibility.
+  static className = 'SGD';  // Note: Name matters for Python compatibility.
   protected c: Scalar;
 
   constructor(protected learningRate: number) {