CLI: config-help still uses -l instead of -g

Created by: jmini

With https://github.com/OpenAPITools/openapi-generator/pull/57 the --lang (short: -l) option was deprecated and replaced with --generator-name (short: -g)

In the config-help command, this was not changed and is not not consistent.

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java -jar openapi-generator-cli.jar config-help -g spring

Should be OK but returns:

Exception in thread "main" io.airlift.airline.ParseArgumentsUnexpectedException: Found unexpected parameters: [-g, spring]
	at io.airlift.airline.Cli.validate(Cli.java:148)
	at io.airlift.airline.Cli.parse(Cli.java:116)
	at io.airlift.airline.Cli.parse(Cli.java:97)

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Empty command:

java -jar openapi-generator-cli.jar config-help

Returns:

[error] Required option '-l' is missing