fix: Random must not be instantiated for multiple invocations

The default seed for `Random` is clock based, meaning that instantiating
`Random` multiple times will produce identical values if the clock
doesn't change. Use the global shared generator instead for
`#newTravisID`.

repository/SmalltalkCI-Pharo-Core.package/SmalltalkCIPharo11.class/class/newTravisID.st

@@ -1,6 +1,4 @@
 instance creation
 newTravisID
 	"Random and image-specific identifier for Travis folds"
-	| r |
-	r := Random new.
-	^ (ByteArray with: (r nextInteger: 255) with: (r nextInteger: 255)) hex
+	^ (ByteArray with: 255 atRandom with: 255 atRandom) hex