[kotlin] Fix code samples and build

Author: harsha509

examples/kotlin/src/test/kotlin/dev/selenium/actions_api/ActionsTest.kt

@@ -47,7 +47,7 @@ class ActionsTest : BaseTest() {
         (driver as RemoteWebDriver).resetInputState()
 
         actions.sendKeys("a").perform()
-        Assertions.assertEquals("A", clickable.getAttribute("value").get(0).toString())
-        Assertions.assertEquals("a", clickable.getAttribute("value").get(1).toString())
+        Assertions.assertEquals("A", clickable.getAttribute("value")!!.get(0).toString())
+        Assertions.assertEquals("a", clickable.getAttribute("value")!!.get(1).toString())
     }
 }

examples/kotlin/src/test/kotlin/dev/selenium/actions_api/MouseTest.kt

@@ -37,7 +37,7 @@ class MouseTest : BaseTest() {
                 .click(clickable)
                 .perform()
 
-        Assertions.assertTrue(driver.getCurrentUrl().contains("resultPage.html"))
+        Assertions.assertTrue(driver.getCurrentUrl()!!.contains("resultPage.html"))
     }
 
     @Test