Improve the Adam optimizer's quality

[ProGamerGov]

Source: https://github.com/jcjohnson/neural-style/wiki/Fine-Tuning-The-Adam-Optimizer

Examples:

https://github.com/jcjohnson/neural-style/issues/428#issuecomment-342691522

https://i.imgur.com/iIRLvKZ.png

These parameters have also been tested with numerous other individuals and their own customized sets of normal Neural-Style parameter values. These individuals found that the new Adam parameters were a lot more like their L-BFGS results, than the old Adam parameters.

[ProGamerGov]

@jcjohnson The default Adam parameters do not appear to be stable with some kinds of style images. These new parameter values seem to be stable with every style image that I tested them with.