fix update examples in sql expression tutorial

[Mike Bayer]

show an example of an executemany() with update, and also a dictionary is never needed in values() - just show straight kw args

[Mike Bayer]

part of this was already done weeks ago, just added some more formatting and an executemany example in 60c9d3daae7586bd12c4ec77a10f3bc0275ca1de

[Mike Bayer]

Removing milestone: 0.6.0 (automated comment)