resolutiondate field in JIRA mapping will be now indexed - Closes #128

To release this change the following steps need to be applied:
1. stop jira indexer:
`curl --user <login>:<password> -X POST '<DCP_URL>/v1/rest/indexer/jbossorg_jira_issue/_stop'`
2. delete mapping:
`curl --user <login>:<password> -XDELETE '<ES_API_URL>/data_jbossorg_jira/jbossorg_jira_issue'`
3. push mapping:
`sh init_mapping.sh data_jbossorg_jira/jbossorg_jira_issue.json <ES_API_URL> <LOGIN> <PASSWORD>`
4. start river:
`curl --user <login>:<password> -X POST '<DCP_URL>/v1/rest/indexer/jbossorg_jira_issue/_restart'`
5. force reindex:
`curl --user <login>:<password> -X POST '<DCP_URL>/v1/rest/indexer/jbossorg_jira_issue/_force_reindex'`