As in HTML report, please add retryCount in JSON report

[dibyaranjan-pg]

As requested in this ticket: getgauge/html-report#259
please also add the same functionality for JSON report.
maxRetryCount as property in Scenario json schema under specResults.

Gauge version: 1.0.7

Plugins

html-report (4.0.10)
java (0.7.7)
json-report (0.3.3)
screenshot (0.0.1)
xml-report (0.2.3)