`_` considered as invalid char in package names

[mohamnag]

according to this _ is a valid char in package names but adding following line in io.vertx.test.codegen.CaseTest#testParseQualifiedCase:

parseQualifiedCase("foo.bar.juu_oo", "foo", "bar", "juu_oo");

will result in a failed test result:

-------------------------------------------------------------------------------
Test set: io.vertx.test.codegen.CaseTest
-------------------------------------------------------------------------------
Tests run: 10, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.001 sec <<< FAILURE! - in io.vertx.test.codegen.CaseTest
testParseQualifiedCase(io.vertx.test.codegen.CaseTest)  Time elapsed: 0.001 sec  <<< ERROR!
java.lang.IllegalArgumentException: Invalid qualified case:foo.bar.juu_oo
	at io.vertx.codegen.QualifiedCase.parse(QualifiedCase.java:35)
	at io.vertx.test.codegen.CaseTest.parseCase(CaseTest.java:178)
	at io.vertx.test.codegen.CaseTest.parseQualifiedCase(CaseTest.java:166)
	at io.vertx.test.codegen.CaseTest.testParseQualifiedCase(CaseTest.java:65)