Travis: also build on Java 9 to detect compatibility issues
Travis: also build on Java 9 to detect compatibility issues

JFormDesigner/RichTextFX,JordanMartinez/RichTextFX,afester/RichTextFX,afester/RichTextFX,FXMisc/RichTextFX,FXMisc/RichTextFX,JordanMartinez/RichTextFX,TomasMikula/RichTextFX,JFormDesigner/RichTextFX,TomasMikula/RichTextFX