Update pom.xml so circleci test will pass. JDK 11 not allowed currently.

Author: michael-w-williams

examples/string-reverse/pom.xml

@@ -57,8 +57,8 @@
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>3.3</version>
                 <configuration>
-                    <source>11</source>
-                    <target>11</target>
+                    <source>8</source>
+                    <target>8</target>
                 </configuration>
             </plugin>
             <plugin>