Use of deprecated Buffer in example code

[Debjeet Biswas]

Following example code are using Buffer which has been deprecated since node@6.0.0

• ./examples/2-datatypes.js
• ./examples/4-cursors.js
• ./examples/8-multiple-cursors-single-transaction.js
• and so on.

Migrate to the newer Buffer.from API so that these examples can be run on newer versions of node.