Reproduction steps:
1. Create the new project with 5.3.5f1 version;
2. Go to Help -> Check for Updates;
3. In the opened window click a button "Download new version";

Actual result: in the window Unity Editor Update Check is written that the new version is 5.4.4f1, although when you go to the page for download the version, it shows to download 5.5.1 version.

Expected result: if it is written that the new version is 5.4.4f1, the page should direct at the page where you can download 5.4.4 version. If the page stays the same, the information about the new version should write 5.5.1 version.

Note: in the 5.5 versions is written that the new version is 5.6.0b3, however in the opened page you already can download 5.6.0b5.

Reproduced with: 5.3.5f1, 5.3.6p4, 5.4.1f1, 5.4.3f1.