Tweak GJF version comment for Maven (#2056 closes #2055)

Author: nedtwigg

plugin-maven/README.md

@@ -232,7 +232,7 @@ any other maven phase (i.e. compile) then it can be configured as below;
 
 ```xml
 <googleJavaFormat>
-  <version>1.8</version>                      <!-- optional, 1.8 is minimum supported version -->
+  <version>1.8</version>                      <!-- optional, 1.8 is the minimum supported version for Java 11-->
   <style>GOOGLE</style>                       <!-- or AOSP (optional) -->
   <reflowLongStrings>true</reflowLongStrings> <!-- optional -->
   <formatJavadoc>false</formatJavadoc>        <!-- optional -->