Update Migration Guide to point to newer Windup User Guide version

The JBoss EAP migration guide, section "3.1. Use Windup to Analyze Applications for Migration" currently points to the 2.4 version of the Windup User Guide. The current Windup version is 2.7.

Recommend either:

• Updating to point to the 2.7 version
• Updating to point just to the Windup documentation landing page, so that this link doesn't get out of date (and we don't have to keep updating with each Windup release)