[jmxfetch] bump to 0.20.0 (#3726)

Author: arbll

config.py

@@ -43,7 +43,7 @@
 
 # CONSTANTS
 AGENT_VERSION = "5.24.0"
-JMX_VERSION = "0.19.0"
+JMX_VERSION = "0.20.0"
 DATADOG_CONF = "datadog.conf"
 UNIX_CONFIG_PATH = '/etc/dd-agent'
 MAC_CONFIG_PATH = '/opt/datadog-agent/etc'