add * to 'chmod 644 /plugins/jdbc/' to set correct perms on jbdc/

Hi, executing the chmod command in the readme instructions will remove the executable bit on $ES_HOME/plugins/jdbc and it's contents which causes the .jars to not be found by ES and this terrible java error to be thrown: 
'NoClassSettingsException[Failed to load class with value [jdbc]'

I've added an asterisk to the chmod command so it executes on the contents of $ES_HOME/plugins/jdbc/ instead of the directory itself.