Documentation for DEPRECATED environment variable does not match CDK behavior

[Jason Walker]

Description

It appears that the documentation regarding the DEPRECATED environment variable does not match the manner with which CDK behaves:

• The environment variable appears to be JSII_DEPRECATED instead of DEPRECATED
• For CDK to throw an exception, this environment variable should have a value of fail instead of error.

This was tested against CDK v1.148.0

[Chris Rybicki]

Fixed by #416