fix getIssueChangelog() wrong endpoint

[zombieleet]

calling the getChangelog() endpoint with an issueNumber causes the below error

null for uri: https://jira.[company-name].com/rest/api/2/issue/ISSUE-KEY/changelog?startAt=0&maxResults=50

This PR fixes the issue by doing the below

1. add expand property with value of changelog to the query object
2. remove "/changelog" path as a suffix to pathname (/issue/${issueNumber/)

This issue was also present in the dotnet implementation as well, which was fixed using this approach
solidify/jira-azuredevops-migrator#13

[pioug]

They look like two different endpoints:

• https://developer.atlassian.com/cloud/jira/platform/rest/v3/api-group-issues/#api-rest-api-3-issue-issueidorkey-get
• https://developer.atlassian.com/cloud/jira/platform/rest/v3/api-group-issues/#api-rest-api-3-issue-issueidorkey-changelog-get

I am not familiar with Jira API, but I'd prefer to recommend getIssue(..., ..., "changelog") instead of turning getChangelog into an alias of getIssue