Update README.md (#32)

Fixed h2 as Github markdown viewer doesn't seem to like mixing heading syntaxes.

README.md

@@ -1,5 +1,5 @@
 Grails Geb Plugin
-===
+=================
 
 [![Java CI](https://github.com/grails/geb/actions/workflows/gradle.yml/badge.svg)](https://github.com/grails/geb/actions/workflows/gradle.yml)
 
@@ -8,7 +8,8 @@ Geb Functional Testing for Grails® framework
 
 This plugin just provides the Geb dependencies and a `create-functional-test` command for generating Geb tests in a Grails app. For further reference please see the [Geb documentation](http://www.gebish.org)
 
-## Examples
+Examples
+--------
 
 If you are looking for examples check:
 
@@ -17,7 +18,7 @@ If you are looking for examples check:
 or [Grails functional test suite](https://github.com/grails/grails3-functional-tests) where Geb tests are used extensively.
 
 Additional Drivers
-=======
+==================
 
 To setup additional drivers you need to add the driver to your `build.gradle` for example: