Tooltip doesn't take className well

Fix issue #1399

Generated classname concat both custom and own classes without space between em

src/components/tooltip/index.js

@@ -40,7 +40,7 @@ class Tooltip extends PureComponent {
 
     render() {
         const {label, className, htmlFor, ...others} = this.props;
-        const renderedClassName = `${className ? className : ''}${this.buildClassname()}`;
+        const renderedClassName = `${className ? (' ' + className) : ''}${this.buildClassname()}`;
         const tooltipProps = { ...filterProps(others), htmlFor, className: renderedClassName};        
 
         return (