sdks.xml has the URL for the last SDK.
<sdk format="2">
<versionNumber>3.0.7</versionNumber>
<title>Connect IQ SDK 3.0.7</title>
<subtitle>release notes for 3.0.7</subtitle>
<agreement>developer.garmin.com/.../agreement>
<url>
<windows>sdks/connectiq-sdk-win-3.0.6-2018-11-27-33ec0d6.zip</windows>
<mac>sdks/connectiq-sdk-mac-3.0.6-2018-11-27-33ec0d6.dmg</mac>
<linux>sdks/connectiq-sdk-lin-3.0.6-2018-11-27-33ec0d6.zip</linux>
</url>
<releaseDate>December 20, 2018</releaseDate>
</sdk>
The correct url is:
-3.0.7-2018-12-17-efeb3e3