change to apex for better fp16 and multi-gpu support

README.md

@@ -326,7 +326,7 @@ The optimizer accepts the following arguments:
 - `b1` : Adams b1. Default : `0.9`
 - `b2` : Adams b2. Default : `0.999`
 - `e` : Adams epsilon. Default : `1e-6`
-- `weight_decay_rate:` Weight decay. Default : `0.01`
+- `weight_decay:` Weight decay. Default : `0.01`
 - `max_grad_norm` : Maximum norm for the gradients (`-1` means no clipping). Default : `1.0`
 
 ## Examples