remove servlet 3.1.0 mention, support 2.5 (#310)
remove servlet 3.1.0 mention, support 2.5 (#310)


GoogleCloudPlatform/java-docs-samples,jetty-project/java-docs-samples,GoogleCloudPlatform/java-docs-samples,jetty-project/java-docs-samples,GoogleCloudPlatform/java-docs-samples,jetty-project/java-docs-samples,GoogleCloudPlatform/java-docs-samples,tswast/java-docs-samples,tswast/java-docs-samples,GoogleCloudPlatform/java-docs-samples,jetty-project/java-docs-samples,tswast/java-docs-samples,jetty-project/java-docs-samples,GoogleCloudPlatform/java-docs-samples,tswast/java-docs-samples