RFR:[13] XS: JDK-8220249: fix headings in java.compiler

[Jonathan Gibbons]

Please review a trivial doc fix to adjust a heading in the java.compiler 
module.  The heading is changed from <h3> to <h2>.

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8220249

$ hg diff -R open
diff -r fb9541185457 
src/java.compiler/share/classes/javax/annotation/processing/Generated.java
--- 
a/src/java.compiler/share/classes/javax/annotation/processing/Generated.java 
Tue Mar 05 10:35:29 2019 -0800
+++ 
b/src/java.compiler/share/classes/javax/annotation/processing/Generated.java 
Thu Mar 07 12:31:38 2019 -0800
@@ -33,7 +33,7 @@
   * It can also be used to differentiate user written code from 
generated code in
   * a single file.
   *
- * <h3>Examples:</h3>
+ * <h2>Examples:</h2>
   * <pre>
   *   @Generated("com.example.Generator")
   * </pre>