Update the watchOS simulator to Apple Watch Series 3

Author: shahmishal

test/lit.cfg

@@ -117,7 +117,7 @@ def get_simulator_command(run_os, run_cpu, sdk_path):
     elif run_os == 'tvos':
         return "simctl spawn 'Apple TV 4K'"
     elif run_os == 'watchos':
-        return "simctl spawn 'Apple Watch - 42mm'"
+        return "simctl spawn 'Apple Watch Series 3 - 38mm'"
     else:
         lit_config.fatal("Unknown simulator OS %r" % run_os)