Bump JMXFetch version to 0.19.0 (#3711)

Author: nmuesch

config.py

@@ -43,7 +43,7 @@
 
 # CONSTANTS
 AGENT_VERSION = "5.23.0"
-JMX_VERSION = "0.18.1"
+JMX_VERSION = "0.19.0"
 DATADOG_CONF = "datadog.conf"
 UNIX_CONFIG_PATH = '/etc/dd-agent'
 MAC_CONFIG_PATH = '/opt/datadog-agent/etc'