nuclear: update livecheck

The existing `livecheck` block regex could quietly surface unstable
versions that appear to be stable (e.g., `1.2.3` from something like
`v1.2.3-beta1`). This updates the regex to use the standard regex
for Git tags like `1.2.3`/`v1.2.3`, which uses `^`/`$` to restrict
the start/end of the tag.

Casks/n/nuclear.rb

@@ -13,7 +13,7 @@
 
   livecheck do
     url :url
-    regex(/v?(\d+(?:\.\d+)+)/i)
+    regex(/^v?(\d+(?:\.\d+)+)$/i)
   end
 
   app "nuclear.app"