change the use of the handler to the standard format file.method

[JohannesKonings]

As described here https://docs.aws.amazon.com/lambda/latest/dg/runtimes-custom.html the standard of the handler is `file.method´.

_HANDLER – The location to the handler, from the function's configuration. The standard format is file.method, where file is the name of the file without an extension, and method is the name of a method or function that's defined in the file.

Currently the complete file name must be entered.

The following would correspond more to the standard format:

• zcl_handler.clas.run
• zcl_handler.run

This should then be taken into account at this points:

aws-lambda-abap-runtime/runtime.js

Line 4 in 88d291d

const handlerClassString = await transpiler.transpile(process.env._HANDLER, process.env.sourcecode);

aws-lambda-abap-runtime/runtime.js

Line 7 in 88d291d

const evalString = 'new (' + handlerClassString + ')().run(' + event + ')';