replaced '_' by '-' as maven properties separator for site mojo

[abelsromero]

Includes:

• Replaces separator with hyphon as commented by @mojavelinux
• Integration test to validate properties replacement with site mojo

Note: I did no include the idea of adding pom- as prefix. Seems excessive and overly complicated, but I am open to suggestions.

[coveralls]

Coverage remained the same at 60.025% when pulling 4fd994c on abelsromero:use_hyphen_instead_of_underscore_for_maven_properties_separator into d18f999 on asciidoctor:master.

[coveralls]

Coverage remained the same at 60.025% when pulling 4fd994c on abelsromero:use_hyphen_instead_of_underscore_for_maven_properties_separator into d18f999 on asciidoctor:master.

[coveralls]

Coverage remained the same at 60.025% when pulling 4fd994c on abelsromero:use_hyphen_instead_of_underscore_for_maven_properties_separator into d18f999 on asciidoctor:master.