Merge pull request jenkinsci#138 from jeffret-b/remoting-3.40

Update to Remoting 3.40.

README.md

@@ -48,12 +48,9 @@ Optional environment variables:
 
 ### Enabled JNLP protocols
 
-By default, the [JNLP3-connect](https://github.com/jenkinsci/remoting/blob/master/docs/protocols.md#jnlp3-connect) is disabled due to the known stability and scalability issues.
-You can enable this protocol at your own risk using the 
-`JNLP_PROTOCOL_OPTS=-Dorg.jenkinsci.remoting.engine.JnlpProtocol3.disabled=false` property (the protocol should be enabled on the master side as well).
-
-In Jenkins versions starting from `2.27` there is a [JNLP4-connect](https://github.com/jenkinsci/remoting/blob/master/docs/protocols.md#jnlp4-connect) protocol. 
-If you use Jenkins `2.32.x LTS`, it is recommended to enable the protocol on your instance.
+As of version 3.40-1 this image only supports the [JNLP4-connect](https://github.com/jenkinsci/remoting/blob/master/docs/protocols.md#jnlp4-connect) protocol.
+Earlier, long-unsupported protocols have been removed.
+As a result, Jenkins versions prior to 2.32 are no longer supported.
 
 ### Amazon ECS