snapshot-resolution: add a sleep to ensure timestamp change

This test suddenly started failing for no reason at line 25, adding this
sleep seems to have fixed that. Every other publish was preceded by a
sleep in this test, so this makes some sense.

sbt/src/sbt-test/dependency-management/snapshot-resolution/test

@@ -18,6 +18,8 @@ $ sleep 1000
 
 # Now let's try this on the opposite order: pubishLocal => publish
 $ copy-file changes/BadCommon.scala common/src/main/scala/Common.scala
+# Sleep to ensure timestamp change
+$ sleep 1000
 > common/publishLocal
 
 # Force dep resolution to be successful, then compilation to fail