Regex tweaks for Amazon Silk and Mobile Safari

I noticed that newer versions of Amazon Silk were appearing as Google Chrome, and that Mobile Safari was sometimes dropping minor version numbers for patch numbers (e.g. showing 7.4 instead of 7.0.4 or 7.1.4).  Here are fixes for both, including new tests from my log files.
Why is this moved as well? I cannot see this supported by any testcase.