Upgrade to Selenium 3.9.1

Closes gh-12057

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -133,7 +133,7 @@
 		<rxjava.version>1.3.5</rxjava.version>
 		<rxjava-adapter.version>1.2.1</rxjava-adapter.version>
 		<rxjava2.version>2.1.9</rxjava2.version>
-		<selenium.version>3.8.1</selenium.version>
+		<selenium.version>3.9.1</selenium.version>
 		<selenium-htmlunit.version>2.29.2</selenium-htmlunit.version>
 		<sendgrid.version>4.1.2</sendgrid.version>
 		<servlet-api.version>3.1.0</servlet-api.version>