Use "issue" term instead of "ticket" in DocBlocks

[aik099]

What is called by "issue" in JIRA is called differently in other issue trackers:

• task
• bug
• ticket
• ...

Since it's JIRA issue tracker client, then JIRA terminology should be used consistently.

I've found 3 places where ticket term is used instead of issue term in method DocBlock:

• Api::addComment
• Api::getTransitions
• Api::transition