Update manual tanh() result

README.md

@@ -23,7 +23,7 @@ Example use:
 >>> grad_tanh(1.0)               # Evaluate the gradient at x = 1.0
 np.float64(0.39322386648296376)
 >>> (tanh(1.0001) - tanh(0.9999)) / 0.0002  # Compare to finite differences
-0.41997434264973155
+np.float64(0.39322386636453377)
 ```
 
 We can continue to differentiate as many times as we like, and use numpy's